^^
I guess -- if you want to use the GTX275 as PPU, it will be way over kill. But then you cannot SLI two different GPU series. Probably a Fermi would do well..whenever it comes.
If you could tell the RAM model number from the sticker/print/packaging, we could help with the timings and voltages.
Yes the TX750 is the Corsair PSU. But its better suited for Xfire/SLI.