Mindover is right.
XFX is better. I'm using a HD6990 from XFX and I can do the bios overclock without voiding my warranty.
Are you sure a HD5770 is enough for you? If you have the budget I'd recommend a HD6970 or something around that specs.
Also, for you PSU, you'll risk blowing your PSU and the whole computer if you stay with the 250W or 400W. To be safe, go for the Earthwatts 750W
by antec. I've used their 650 watt one in the past and it powered my overclocked EVGA GTX 285 with no problems. Its about 95 dollars.
Are you going to play games like Crysis? To run it on the 1080p screen you would need at least a GTX 570. If your budget allows for it, go for the close to top end GPUs