link the exact cards you are talking about, I have a single slot 5770 that I picked up awhile ago for a backup rig running at 720p and it does just fine. I would say that a 5770 is definatley what you are looking for.
Personally If I were to order one right now id get this one:
and you get dirt 3 for free which looks like a pretty cool game, go to ign and watch the video review...
good luck and have fun, ignore the newegg reviews oftentimes they are way off, Ive owned a couple HIS cards with no issue and I think they have a 3 year warranty. The Single slot ones from XFX (double lifetime warranty) are nice too but I don't think you will be doing any oc'ing with the single slot models, at least my diamond one does not.
In the end the gigabyte model is not worth it and it only offers a 50mhz increase over stock which is likely easily attainable on its own, but at the end of the day the 5770 will handle 95% of games pretty much maxed out at the 12X10 resolution imo
Thanks, That's the HIS 5770 I was refering to. I just read a comparison and the HIS was a little faster than the Gigabyte (only 4%) but the Gigabyte ran cooler due to the 2 fan design. I'll save the $20 and get the HIS.