And yes I'm planning to overclock both the GPU and CPU, just cant pick between using heat sink cooling or water cooling.
More aboutradeon 5770 fire 5830 single
Crossfired HD5770 swap blows with HD5870 in performance.
Personally I would step up from a 5830 and get a 5850, the 5770's in crossfire cost more than that option so it should be within your budget. Your resolution will matter here and if you dont have a monitor capable of 1920x1080 then just get the 5830. Crossfire and SLI while alot better than it used to be is still hit and miss with the performance dependant on Game and Driver support.
This is the one I was planning to get. As far as Memory clock and core clock, they are the same. Although the one I want to get is almost $260. I'll do some more research, and try to find out which card is better for overclocking.
If $260 might as well spend extra $30 and get HD5850