what resolution are you gaming at? Also- what PSU do you have. The 5850 and 5870 do use quite a bit more power than the 5770- they require 2 6pin PCI-e power connections as opposed to the 1 on the 5770, though I don't know that I would call it a 'tremendous difference'. They are a bit warmer, but that generally really isn't much of an issue. the 5870 is roughly double the performance of your 5770, so if your mobo and PSU support it, you could always just throw a second 5770 in there.