Gpu upgrade

well with nvidia slashing prices on all their cards i have a predicament, ive got a EVGA GTX 770 classified card and im debating getting a gtx 780 since its down to 500$. now i also though about getting a second 770 and run sli but the problem is id have to upgrade my psu for that. i have a 750 watt. should i get a single 780 and then save up and get another 780 later and run sli since they need only 300 watts each or should i just go ahead and get the 780 ti? and run a single card configuration

770 classified card, you should get a decent amount back if you were to sell it.

After reading all the reviews the 780ti is a beast especially overclocked. Even the stock cooler holds up well. Certainly would be making titan owners feel sorry for themselves.