For Power - Look here.....http://www.tomshardware.com/2007/08/21/energy-efficient_computing_options/page5.html#single_graphics_cards
Seems SLI of your card may require about 350 Watts for those cards.
Add 95w for the TDP of your Q6700. and you have 445watts for the core system and between fans, drives, etc... you may be pushing 500w.
Considering you have a no-name brand PSU, I would think you are borderline at best. If it was a Corsair/Seasonic 620w I would be less concerned.