It may help if you take a look at what resolution you play at, etc. You mentioned you want to play using 3dvision. If you're at 1920x1080 a pair of 560 ti's should be plenty powerful and you won't have the big power consumption you would with a pair of 480s (keep in mind the 480s would be faster).
There are some pretty incredible deals on 560 ti's right now and you could probably find a pair for around $360 or less after MIR. Cheers.