Upgrading from gtx660 to 770sli - cooling and spu

Phil456

Honorable
Dec 27, 2013
4
0
10,510
Hello there, I would like to upgrade my graphic card.

My current setup:
Asus Z87-A
i7-4770k
Asus gtx 660
Semi-passive 550W spu
Fractal design define r4 case


My current setup is very silent and I would like to keep it that way. Im using classic air cooling, having stock case fan in the front and in the back of case, stock cpu cooler.

So here come my questions:

Which spu would you reccommend to run 2 gtx 770s? I understand 2 cards require more power but I wouldnt like to overkill it.
With increased heat from 2 cards, do I have to upgrade my current cooling setup? Excuse me, Im no expert at this, Im talking about adding one more front-fan or getting non-stock cpu cooler (if heat from 2 cards affects it in any way).