What's your monitor's resolution? That's extremely important to know for choosing the GPU. If it's 1900x, you should really try to fit in the HD 5850. If you were to drop down to the X4 620, you could fit it in the budget (including the changes below)
Case/PSU: Antec 300 Illusion and Antec Earthwatts 500W for $120. You don't need that large of a case for the 5770. The 300 can fit up to the 5850 comfortably, and the 5870 with some effort. OCZ isn't exactly a high quality PSU maker, and this Antec unit is better for about the same price. 600W isn't need for a single GPU, especially a 5xxx series card.
HDD: WD is slow right now. Grab the Samsung Spinpoint F3 1 TB for $90.
RAM: Spend the extra few bucks for the CL 7 Ripjaws.
If it's just for gaming and no CPU intensive tasks (transcoding, compressing, etc.), the it definitely is worth the sacrfice. But it only matters if you have a 1900x monitor. You likely wouldn't see much difference between the 5770 and 5850 on a 1600x monitor, as you can only see so many FPS anyway.
OK MadAdmiral, I have been doing a little more researching on this site (love it) and I have switched a few things around on my build. I'm going to go with an HD5770 and most likely crossfire another one down the road when I need some more juice b/c I checked my monitor and it runs 1620x1050 and I think a HD5850 would be overkill for this resolution. Here is what I updated...