Son of a Zombie :
My intel EXTREME mobo operates in pcie2 x16 with 1 card, but x8 with 2 cards. I want to get 2 x Gigabyte GTX 760 OC 4GB cards but am very concerned about saturation/bottlenecking. If there is saturation, what is the most bad-ass pair of cards for pci-e2.0 x8?
imo 4 GB version 760 cards are worth the extra money. But for all of the newest DX11 games (BF4 is the only exception) your best off using Adaptive V-Sync and FXAA. And FXAA makes 4 GB unnecessary. Adaptive V-Sync works just like regular V-Sync; which will stop the Micro-stutter effects by capping the Max FPS to your monitors frequency. (60 Hz for most ppl, but many have 120 Hz and even 144 Hz now.). But unlike traditional V-Sync, adaptive V-Sync will also briefly disable itself to avoid the FPS from dropping to 1/2 of your monitors Hz. FPS can even drop to 1/2 of 1/2 with traditional V-Sync. Without any V-Sync the FPS can leap and jump too high for the shortest intervals of time and makes an effect that ppl refer to as micro-stutter. V-sync eliminates it. But many ppl don't appreciate having no other resort. Remember to use Adaptive V-Sync from the NVCP game profile for each game.
FXAA results in an average of 50% better performance versus traditional AA. And FXAA looks fantastic. If you did a blind test (ppl tested were unaware and had no clue of wat the setting was set to), then it is very hard to see the difference between FXAA and traditional AA. (But remember the 50% better performance with FXAA!) In fact, once you use some of the performance gains (average of 50% better) to tweak the game's profile in NVCP's game profile for a game and enable anything that improves the picture quality, then you still have an improved FPS with FXAA and everything looks as good as traditional AA if not even better when considering the FPS is much higher. If FPS was equal then you could argue in favor of traditional AA versus FXAA. To achieve it you'd have to spend much more money on a vid card(s).
But here's the really big 4 GB card using FXAA, irony. FXAA reduces to amount of vRAM used between 25% and 50%. Therefore on 1080p and even 1440p, while using FXAA, there's no need for more than 2 GB. And even if you did use traditional AA and all the settings to use more than 2 GB on said set-up, the FPS; because of the bandwidth of the 760 (256-bit); would be so low it would be unplayable.
So here's a few scenarios for needing 4 GB card(s). First off is that it is not that much more expensive. And seeing how you can't upgrade the vRAM after you buy the card(s), then why not just get it. Mind you, not that you need it, but rather than future-proofing alone, you're just buying it for bragging rights. Second is that it's a fact that if you install mods for games designed to increase the eye-candy (like Skyrim mods or Crysis mods) then you definitely can use 4 GB on said set-up.
And if you play BF4 99% of the time, go with a single vid card. Especially since the price of 780 has dropped and it is the same as two 760 cards. And a 780 will run BF4 smoothly whereby with 760-SLI it stutters even with V-Sync. Maybe, drivers or game patches will fix this problem. But when, if ever, nobody knows. If you play BF4 some of the time and many other DX11 games, then 760-SLI is better because you have two cards to use later on after you upgrade one day to a GTX 800 series card or cards. Unless you are into selling cards, two 760 cards for back-up or use on another PC is a better investment, too.
GL