Well a 780ti is a big performance boost over SLI 760's. 760's perform very well in SLI however if you have another $300 to blow go ahead. You are probably going to be a little over a GTX 780 with SLI 760's, probably easing up on 780ti speed however your going to be drawing more juice with SLI 760's and some games don't support SLI so your going to be running some of your games on a single 760. Just keep that in mind
Note: Seasonic has a 1000w PLATINUM Modular PSU on Newegg right now on SALE for $139.99, thats how much I paid for my Seasonic 750w so if I were u I would be stretching my $$$ and going for that....
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