Oh and yes, already checked that, it's fine, the power consumption for these cards are very good I hear, only two 6 pins? I upgraded my PSU already so should be able to handle it
750 watter should be fine for SLI'ing two 670's ...... I'd use an 850 watter though if using non-refercne cards and your planning to go for significant OC's.
Guru3D took their Asus 670 TOP to a boost clock of 1280 (915 is reference). It should draw about 180 watts at that speed....149 is typical for a reference card. Overclocking a 2500k to say 4.7 Ghz will add about 42 watts....
So for a overclocked CPU and overclocked twin GPU's, I'd want (31 + 31 + 42) 104 more watts than a stock box.