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personally i would upgrade to i7 but you can see for your self here.
id say no , just came to an e8400 @ 4.00 ghz and its the fastest thing i have witnessed after messing around with quads , excessive heat , endless hours of fine tuning in bios etc. Only thing you need is a dead overclocked core2duo these days. Id say get an i7 when they switch to 32nm , DDR3 would be cheaper by then too
Obviously you havent had the pleasure of testing an i7 rig then, because i know you'd be saying the opposite.
if you feel you need to upgrade then better get the Q9550 , but honestly you are fine at 4.00 ghz with your E8400. I had a Q6600 @ 3.4 and the E8400 beats him in everything bar video encoding

wrong i had the pleasure of playing with i7 but the platform has some major disadvantages at the moment such as
1.price
2.heat output
3.problematic motherboards
1 : Price for a i7 920 is similar to Q9550
ok you named 2 games in a total of ...50lets say? There is still plenty of work to do by the developers.
Ofcourse the i7 will beat the seven bells of the E8400 but it wasnt my point overall speed , its more of reasonable choice keeping the E8400 as it is more than enough for todays needs, you disagree?
ALso by the time quads will be used widely by software your quad will be history , he will then have the chance to buy the best quad (or octacore) saving money in the meantime from unnecessary upgrading .
he didnt buy them , he said IF he bought them. And tbh a single 4870X2 is more than enough , heck i am gaming with a GTX260 and i have no problems whatsoever