why 1gb?just get 512mb,1gb memory on it is a waste.your pc will run games fine at 1600x900 but donot expect on high settings.and donot even think to use directx11 with it.i used it and it made me cry.10fps on 1600x1200 with dirt 2 on high.how sick is that.i really hate it,even my 8800gt is better.why not you buy hd 5750 or hd 5770 or gts 250?
really tough?only 18amps?my 400watts psu has 25amps and i am running 8800gt smoothly.can max out any game i want at 1280x1024 including crysis with 15 to 30fps.well i think hd 5670 only suits you.but it is 5 to 10 percent slower than 8800gt/9800gt.
but why to buy hd 5670 when 9800gt and 8800gt is available in a low price.the directx11 on that card is just like having pentium 3 with ssse3 feature.its not worth card to run directx10,9800gt and 8800gt always beats it by 10 to 20 % difference.why not you upgrade to a psu with 24amps even a 400watts.it will run 9800gt/8800gt very well.i am using 8800gt with 350watts retail plus power supply believe me its awesome.it runs very good.it has 22amps.
i think the problem is PSU. the safe bet is to get 5670 since the card only draw power from the pci-e slot. to OP: if you don't care about dx11 then just go for 5670. but if you care maybe you should get better PSU and HD5770. if you're worried about 5770 being bottleneck by your cpu then just OC your cpu a bit