It's generally on par with the 4870, although in quite a few tests the 5770 is outpaced by the older card.
However, if you're ok with waiting for a couple weeks, ATI will be debuting the 5830, which will take the 4890's place. The card is projected to come in just under the $200 mark. It'll be way overkill for playing at 1440x900, but then when you grab a new monitor that has a higher resolution, you'll be all set to go, instead of having to buy a second 5770 and Crossfiring. Chances are, you'd be money ahead with this route.