From what I've read in professional reviews, the 768Mb and 1Gb versions of the GTX 460 are only slightly different. The difference is quite negligible, imo.
But from what I've heard other people say, the 1Gb version starts to make a difference if you're playing on super high resolutions (read: 3 monitor set up). Unless you're doing something crazy like that, you won't notice a difference between the two versions just by eyeballing them.
I'm about to leave home any minute now to go buy my parts. The only 1Gb version of the GTX 460 available where I live is the one from Palit. And the factory overclocked one is arguably the fastest factory setting GTX 460 on the market right now. The draw back is that it runs pretty **** hot (79 degrees on stress tests).
What I'm going to be buying is the EVGA 768Mb factory overclocked version. When you overclock both these cards further to what you can with stock voltage, the performances are very close.
However, the EVGA runs WAY cooler (60ish degrees on full load). Therefore, there is more room for overvolting, and thus more room for further overclocking. Ultimately, the EVGA 768Mb could very well outperform the Palit 1Gb. And it's quite a bit cheaper, too.
I'll be getting my parts today. Gonna take a few days for the thermal paste to cure before I can really start pushing everything. We'll see how it goes.
Edited, Aug 7th 2010 2:32am by Threx