I just ordered a used GTX470 (super clocked) to upgrade my GTX275. The main reason was for GPGPU compute in matlab (only works with nVidia and needs double precision). The card is still in the mail but now I am wondering if the PSU will take it. I see the TDP is rated about the same as the GTX275 but I have seen reviews showing power consumption in a system a bit higher. A kill-a-watt meter reports my system is drawing about 202W (including one 19" LCD) while typing this out with notihing really running.
C2Q Q6600 @ 3ghz (Sandra reports 99.8W)
8GB DDR3 1600
GTX275 (going to swap for GTX470SC)
90GB SSD Vertex2
1TB WD 7200rpm
3 x 80mm case fan
1 dvd burner
1 fan controller
Corsair HX520W PSU <-- Will this cut it?