Well...here we have it from a well respected test site.
I dunno if these figures are true or not but read the WHOLE article and you will see that as far as they are concerned, the extra memory was of little consequence and its drivers that are the key.
Even in Crysis, with the new set of drivers, the 640mb version will give no performance boost over the 320mb. So, at resolutions on screens 24" + there may be a difference (i couldnt find a test to prove or disprove this). On a screnn 22" and under, regardless of the game you play, whether its PacMan or Crysis, the 640mb version is no better (and in a few instances worse, then the 320mb.
See here: http://www.xbitlabs.com/articles/vid...oundup_17.html
In fact, in STALKER, the 320mb version actually performs BETTER @ 1600x1200 and 1280x1024 .
All 3d Mark Score differences are negligible aswell.
From what i can see, the GTX and Ultras (little diff between these), do stand out well, but 320mb vs 640mb is well and truly blown now if this review is to be taken as read (no reaon why it shouldnt be).
Looking at it then, it was just a driver issue and not having them optimized correctly which formed the myth that the 320mb took a performance hit over the 640mb.
In the end, i dunno if i believe what they are saying or not as, like with most reviews you read, there is alot of conflicting evidence.