@Terabyte
If you have budget problem... you go ahead with card only for now.. But there is no headroom for you anymore. your chances for any more devices will get SLIM for now.... Later when chance is there ,sell and buy NEW SMPS like topgear suggested go for it...
If you buy only CARD now,, Please provide your input by playing GPU intense games like Metro 2033, Warhead, Bad Company 2 in Max settings especially with AA and AF (if no AA and AF, Card is not bothered to run hard).. Make sure you run them very long ....
Also what's your Monitor, DID i miss anywhere? If your resolution is below 1680x1050, especially 1280x1024, you don't have to worry about SMPS ,becoz below that GPU is capped to limit with high end Vid cards and games depend on more CPU.. Vid cards stress only above 1680x1050 especially from 1920x1080(1200)... where CPU lacks such bandwidth to support in higher resolution.. Here OC your CPU plays key role... especially in SLI.