The amount of memory usually has a direct correlation to how well the card handles different resolutions. Back when 8800GTS's were in demand, I remember buying just the 320MB version because I ran a low res. From what I understand 512MB is usually enough for the ATI cards. I think the Nvidia cards need more memory because of their architecture. What specific card are you looking at?
TBH if I only played at 1024x768 I'd get the card with the most memory. The higher you can make the games settings makes them nicer to look at and you don't have the fear of choppiness or stutter. Not to mention how much it will help with explosions and shadows and such.
Not sure I like a card where more than 10% of the reviewers pan it. Look for another.
It's a little more expensive than some others, but 4870s are known to run pretty hot. That's why I wanted to make sure I got one with a good cooling system. I considered the Dark Knight one a lot too, but for some reason I just didn't like it as much.
I gotta laugh. I looked at your original thought and while I was at newegg today all the "old' reviews were gone and now only good ones appear. Those guys are real scumbags. We're not going to be able to get honest opinions by ALL the users any more.