ATI 5770's

ALL 5770s are 1024mb as far as I know, and if it exists then it's not recommended due to being a unnoficial card and having potential design flaws and driver problems.

Depends on the resolution and settings (higher resolutions and Higher settings like AA, AF etc. use more RAM) that you will be using and the games\programs you will be using -- but in most cases the price difference is only $10+/- so I'd get the 1gb. standard version to avoid it being a problem.

EDIT : @ wiinippongamer - the 512mb. versions have been available since shortly after release (at that time there was a greater price difference which made them a viable option but the cost of an extra 512MB of DDR5 memory is now so small that they no longer make much sense so only one or 2 manufacturers still offer them.) For Example : This PowerColor Model

Didn't know that, can't see any on newegg nor amazon though.

But yea it's just not worth it because of such a small price increase