2x780ti, I recommend msi lightning. But will be a lot easier to sli without glitches/artifacts with 2 cards vs 3. You'd need a board with 3 pcie slots, preferably all at 16 or 8x. And you'd need a power supply capable of handling over 1000w of just gpu power draw. Vs, running two just beastly cards, only needing 2 slots which is very common even in high budget boards, and psu limits would also be drastically lower. As well as heat, and fan noise. Plus, like you said, you could always add a third down the road if/when you might ever need (which I more than highly doubt 'need' over want for bragging rights)