phailer7 :
The 770 has a 4gb model which is more than the 780's 3gb... so 3-Way Sli 770's at 4gb Vram each, one of them designated to physX only, is a much better performer and costs around the same as 2-way Sli 780's.
Are you just pulling this out of your butt?
For one thing, nothing is currently limited by 3GB vram, not even close (modded skyrim doesn't count, it can supposedly be made to have problems with 4GB as well). Also, dedicating a card to PhysX is a terrible idea that would basically defeat the purpose of 3-way SLI.
Annnnnnnnnnnnnnnnnnnnd finally, 3 770s is not going to beat 2 780s in any appreciable way:
That's for 2x Titan vs 3x 680 but the 770 is close enough to the 680 and the 780 close enough to the Titan that it's generally applicable here as well.
OP, a pair of 780s is a far better option than 3 770s. Similar performance, fewer driver issues, less heat, less noise, more vram. Do note that you shouldn't be considering any of these options for less than 1440p resolution, as others have pointed out, and know that this type of power is really only needed for maxing out Crysis 3 at the moment.