770 sli'd would be alot better than a 780 alone but you have to take into consideration power consumption and also you have to make sure the games you wish to player if this is for gaming that the games are compatible with SLI or else it can be completely useless while playing those games in some case completely unplayable unless you remove the SLI. another issue would be that you would need to make sure you have enough power as 2 770 will require quite a decent power supply best bet would be to use a power consumption calculator like http://extreme.outervision.com/psucalculatorlite.jsp.