People always say a single card = best solution but it's not true.
Buying New:
If you have a 4870 for example, and are then faced with the decision of a 300 pounds 5870 or another 4870 in crossfire for 100 quid, you can get the second 4870, have competative performance to the 5870, granted you don't have DX11 or eyeinfinity and a higher power draw and slightly higher temperatures, but you're saving yourself 200 pounds.
People only poo poo the previous power draws and temperatures as soon as something new comes out with lower ones, yet previously when those cards came out they were the thing to have. The same thing will happen with 58XX series, 6XXX series will come out and people will poo poo the 5XXX series draw and temperature.
On top of that, if you haven't got money to throw around and have to wait for a card to come down to 150ish quid before you'll buy it. In the example I gave before, having one 4870 - lets say you bought it for 150 quid - and then buying a second one now for 100 quid, will in total have cost you 250 and you'll be able to continue playing your game on maximum settings, and won't need to upgrade until a single card which can beat your dual cards - likely the 5890, seeing as 4870x2 is on par with 5870 - is out and comes down to 150 quid. Now you will have upgraded from a crossfire setup matching 5870 performance - albeit without the new tech which is scarcely supported yet anyway - to a single card more powerful.
Now on the other hand you bought a 4870 at 150 quid which you still have. A 5850 might come down to 150 quid in 6 months, so between the card you have now and the 5850, you'll have spent 300 quid and still dont have the same frame rate as 2x 4870s (which would have saved you 50 quid) and it means you're going to have to upgrade sooner anyway, than if you had just bought a second 4870. Meaning more money, sooner.
And let's not forget that in the meanwhile, you're waiting for the next card to come down to 150 quid, you aren't able to play games at highest settings because you have a single card worth around 100 pounds. And waiting for the card 2 up from yours to come down to 150 pounds is going to put your current card below 100. Look at the cards currently below 100, why settle for that when you can save money, play at higher fps, higher settings at the cost of a little extra power draw, and a little higher temperature, which a year ago nobody batted an eyelid at.
Buying/Selling Second Hand
In the idea that second hand cards go for 50 quid under shop value to make this easier:
Okay let's say you buy a 5850 at 200, and it comes down to 150 quid. The 5870 has also come down 50 quid.
You flog your 5850 at 100 pounds, and are able to put up another 100 for a 5870 totalling 200 (second hand value) and costing you in reality 100.
You've practically bought this 5870 for a release worth of 300 pounds now.
On the other hand you buy a second hand 5850 at 100 pounds to crossfire with your current one.
You've now also spent 300 pounds in total but have better performance than the 5870.
Keeping with the idea that the cards go second hand 50 quid under what they are in the shop;
The 5870 comes down another 50 to 200 pounds, you're able to sell it for 150 pounds. A new card is out costing 300, you put 150 with the money you got for the 5870 and purchase the new card. Forgetting all previous money spent, you've bought this new card for 150 quid.
The 5850's you previously crossfired are likely to have similar performance as this new card much like the 4870s have with the 5870 - so no upgrade necessary.
You're now back at starting point. The crossfire 5850's have little value - 50 quid each. The new card you've bought will have greater value but you've already spent 150 quid extra to obtain it.
Assuming you sold both the 5850's as soon as you crossfired them, and the new card you just bought as soon as you bought it.
You sell the 5850s 50 quid each for a total of 100 pounds.
The new card for a total of 250 pounds - deduct what you bought it for - 150 pounds, and you have gained back 100 pounds.
Complete neutrality.
And the cycle starts over.
Buying new, 2 cards are better than one.
Buying second hand, it's pretty much level ground.
Buying New:
If you have a 4870 for example, and are then faced with the decision of a 300 pounds 5870 or another 4870 in crossfire for 100 quid, you can get the second 4870, have competative performance to the 5870, granted you don't have DX11 or eyeinfinity and a higher power draw and slightly higher temperatures, but you're saving yourself 200 pounds.
People only poo poo the previous power draws and temperatures as soon as something new comes out with lower ones, yet previously when those cards came out they were the thing to have. The same thing will happen with 58XX series, 6XXX series will come out and people will poo poo the 5XXX series draw and temperature.
On top of that, if you haven't got money to throw around and have to wait for a card to come down to 150ish quid before you'll buy it. In the example I gave before, having one 4870 - lets say you bought it for 150 quid - and then buying a second one now for 100 quid, will in total have cost you 250 and you'll be able to continue playing your game on maximum settings, and won't need to upgrade until a single card which can beat your dual cards - likely the 5890, seeing as 4870x2 is on par with 5870 - is out and comes down to 150 quid. Now you will have upgraded from a crossfire setup matching 5870 performance - albeit without the new tech which is scarcely supported yet anyway - to a single card more powerful.
Now on the other hand you bought a 4870 at 150 quid which you still have. A 5850 might come down to 150 quid in 6 months, so between the card you have now and the 5850, you'll have spent 300 quid and still dont have the same frame rate as 2x 4870s (which would have saved you 50 quid) and it means you're going to have to upgrade sooner anyway, than if you had just bought a second 4870. Meaning more money, sooner.
And let's not forget that in the meanwhile, you're waiting for the next card to come down to 150 quid, you aren't able to play games at highest settings because you have a single card worth around 100 pounds. And waiting for the card 2 up from yours to come down to 150 pounds is going to put your current card below 100. Look at the cards currently below 100, why settle for that when you can save money, play at higher fps, higher settings at the cost of a little extra power draw, and a little higher temperature, which a year ago nobody batted an eyelid at.
Buying/Selling Second Hand
In the idea that second hand cards go for 50 quid under shop value to make this easier:
Okay let's say you buy a 5850 at 200, and it comes down to 150 quid. The 5870 has also come down 50 quid.
You flog your 5850 at 100 pounds, and are able to put up another 100 for a 5870 totalling 200 (second hand value) and costing you in reality 100.
You've practically bought this 5870 for a release worth of 300 pounds now.
On the other hand you buy a second hand 5850 at 100 pounds to crossfire with your current one.
You've now also spent 300 pounds in total but have better performance than the 5870.
Keeping with the idea that the cards go second hand 50 quid under what they are in the shop;
The 5870 comes down another 50 to 200 pounds, you're able to sell it for 150 pounds. A new card is out costing 300, you put 150 with the money you got for the 5870 and purchase the new card. Forgetting all previous money spent, you've bought this new card for 150 quid.
The 5850's you previously crossfired are likely to have similar performance as this new card much like the 4870s have with the 5870 - so no upgrade necessary.
You're now back at starting point. The crossfire 5850's have little value - 50 quid each. The new card you've bought will have greater value but you've already spent 150 quid extra to obtain it.
Assuming you sold both the 5850's as soon as you crossfired them, and the new card you just bought as soon as you bought it.
You sell the 5850s 50 quid each for a total of 100 pounds.
The new card for a total of 250 pounds - deduct what you bought it for - 150 pounds, and you have gained back 100 pounds.
Complete neutrality.
And the cycle starts over.
Buying new, 2 cards are better than one.
Buying second hand, it's pretty much level ground.
