Sorry that I didn't see this sooner.
Actually, you're not asking for too much at all. Not for $150 or less. This
is easily the most powerful card that your PSU can handle. It's quite a bit faster than either of those other cards that you linked to and it's within your budget. You can get an additional 2% off if you have a Windows Live ID and go to Newegg via Bing Shopping, making the final price $117.29.
EDIT: I'll keep you up to date when I find new deals if you want. I may be able to find a 1GB model for not much more if you want a bigger frame buffer. The 5770 is definitely the
card to get in your price range that will run on your power supply.
"They should rename the team to the Washington Government Sucks. Put Obama on the helmet. Line the entire walls of the stadium with the actual text of the ACA.
Fix their home team score on the board to the debt clock, they can win every game 17,000,000,000,000 to 24. Losing team gets taxed by the IRS 100%, then droned."