Hardware lurkers - help me find a new video card!

[Concillian]

I don't want to spend a heck of a lot of money to replace it because my system isn't that great (Core2Duo e8400, 4GB ram), but I figure there must be a decent value video card that at least matches or exceeds the performance of the 4890. Ideally I'd like something really quiet and low-power. I've looked into the 6770, but I really think it's overkill for the rest of my system.

6770 is a little slower than the 4890... it's pretty close. If you're looking at reviews to compare, look at the 5770, since it's the same card as the 6770. There should be plenty of reviews that have a 5770 head to head with a 4870 and some with a 4890.

6850 is the definitely faster, 7770 is kinda in-between 6850 and 6770, but uses less power. 7750 is about the same as the 6770, but uses less power. A 6770 alone is a very significant power consumption difference. 5 series had much better idle power consumption than 4 series. 7 series is again better, but not as significant as 4 --> 5/6. 6850 should still use significantly less power than a 4890.

There's basically no nVidia cards worth looking at in that price category. Unless there's still 460s leftover, they overclock well, but do consume a fair bit of power doing it. If staying at stock speed, just forget about nVidia in this price range.