PCIe x16 and x8 and SLI, VGA's and PSU's

Hardware Hub Motherboards
1
Hey everybody, what I know is that PCIe x16 is the fastest way of connectivity, but I was in a hassle of buying one EVGA GTX780 SC ACX or two EVGA GTX 760 SC ACX in SLI, and after some benchmarks online I found out the 2 760's would give a Titan a run for it's money, and they totally beat the single 780, so after days of research I decided to go with 2 760's and I want to get a Z87 Sabertooth Motherboard, but while going through the specs, I found out that two PCIe will run at x8 each not x16, so right now i am in a new hassle! does this slow down the cards? or how does it work? can someone please explain this in detail??
 
 
and Which do you think is better generally?
 
 
1 EVGA GTX780 SC ACX
2 EVGA GTX 760 SC ACX in SLI
1 ASUS GTX 780 DirectCU II
2 ASUS GTX 760 DirectCU II in SLI
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ASUS Z87 Sabertooth with i7-4770K
ASUS Maximus VI Hero with i7-4770K


and Will a Corsair GS800 Run 2 GTX 760's?


Thanks everybody in Advance.
2

well x8 and x8 is GEN 3  is equal to x16 x16 pci-e 2.0. so yeah it would absolutley fine.

i´m personaly more prefer a single GPU setup, in that case a GTX780 is a realy great value for the money. but yeah on the otherhand 2 GTX760´s super clocked will cost arround $512 so thats cheap, if they realy beat a GTX780???..

3

They will beat a GTX 780, but with the 780, you're paying for the reduced temps/noise/power consumption/ease of having a single card and not having to deal with any issues put forth by SLI.

4

SLi/Xfire have the ability to be both amazing and the most annoying thing youve ever used, all at the same time :P