I am looking for a bit of advice. My current system is athlon x4 635 with geforce gt 220 and a cheap 450w psu with 20A on 12v rails. I game at 1368 x 768 resolution and don't need uber performance for highest settings/AA and stuff. Since my budget at this time is quite limited I'm looking to get only a gpu for now and upgrade the rest later. Here in the UK I can get XFX/Gigabyte 7770 or XFX 6850 for about 100 pounds. I read that 6850 is slightly faster but also slightly more power hungry. I will get a decent psu in a month or two but will it work for me till then with 6850? I can't decide if 6850 is faster by enough to warrant a new psu right a way, I would really prefer to buy it a little later. Any advice appreciated.
I wish i knew how they can make so many 450 watt power supplies with less power then a mid quality 300 watt unit.
Power requirements fully depend on the rest of the system. With a light 65-95 watt cpu chances are you can pull it off, but if the power supply fails it may or may not take other stuff with it when it goes.
The 7770 is one of the BEST lower powered cards you can get coming in just over 80 watts if you hit it with fur-marks.