if your planning on building a new rig in the summer, i'd hold off on getting a new psu until its necessary. keep an eye on the corsair 520 (which has been one of the best psu's to get for the last 3 years), see if they have a special or something in the next month or 2.
and i found some insight. the 9800gt, is nearly identical to the 8800gt, just uses a touch less power. 108w under max load. that is 9a at 12v. so 2 of them gives you 18 amps on 12v. if your cpu is rated at 125w, (phenom II quad) 10.5 more amps, so we are at 29 amps minimum on the 12v rail will be sufficient. which is 348w on the 12v rail (or rails). those are the 12v devices.
http://www.tomshardware.com/reviews/Sys ... 62-10.html
is a link where tomshardware ran an overclocked 8800gt SLI system on a 400w psu.
just note that it is a silverstone psu, which, they are one of the top companies for psu's (corsair and antec are up there too). a quality psu that has ample 12v power for your cpu and gpu(s) will power your system.