This is a really interesting thread - largely because it's a bunch of users re-enforcing one another's lack of understanding about what DDR3 delivers over DDR2.
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And before you jump all over me - ask yourself this. Would I buy a performance graphics card with DDR2 RAM in it? I bet you wouldn't. Why? Because the DDR3 cards are much faster.
I wouldn't buy either, simply because graphics cards don't use ddr2 or ddr3.
Clock for clock DDR3 delivers 50% more bandwidth than DDR2, so you could actually go to to CAS8 DDR3 from CAS5 DDR2 before DDR2 outperformed the DDR3 RAM at the same speed. And that's not the REAL benefit. It runs at 1.5V, not 2.2V or 2.4V like the current very high speed DDR2. The big benefit of that is runs much cooler so it's more stable and more reliable.
And DDR3-PC8500 is just the start, there will be DDR3-PC12800 (1600MHz) very soon, still running at 1.5V and with apparently very high latencies.
Indeed, people just looks at the speeds and latency and jump to conclusions, http://en.wikipedia.org/wiki/DDR3 - some interesting info for people who don't know much about this new ram.
All that said - I do think they're having a bit of a laugh with the pricing. Given that for a bit over £100 I can buy a fast graphics card with 512Mb of similar speed DDR3 on it, then 2Gb for £300 looks like
spectacularly (fixed

)greedy pricing.
DDR3 != GDDR3
You cannot compare the prices of graphics cards and the amount of on-board GDDR3 to DDR3 system ram.