What is the psu requirements for evga gtx 780 ti sc,confuse between corsair cx 600 and corsair hx 650,if its OK with 600,I better go for it to save electric bills,my rig:i5 4670k,Asus z97 itx,16 gigs,1 tb.No overclocking and on the other hand i could have go with gtx 970 but my friend is willing to give me his gtx 780 ti at a cheap price