what the ^ since when do you need 8gb of vram for 4k??
I play on. 4k TV using my 980ti, even HUGE games like gtav or witcher 3 don't use more than about 4gb. and then it's even less than that as what the game is telling you its using is actually much higher than real usage, as when there's free space available it'll use it for the sake of it.
he'll even my 970s used to play 4k games with only 3.5gb of vram, that's also why many never notice the .5 vram issue with them as they don't actually go into that last bit of vram properly.
sli has pros and cons, a simple way to put it is.
more heat (can get toasty if running both at max)
more power consumption therefor a larger psu required.
sli can *sometimes* not be supported, or supported very poorly, doom had a statement when it came out apologising for the lack of sli support and that a patch would fix it.
even some games that support it, may not scale well, meaning you only get a 20-30% performance boost.
on the plus side
sli when it does work can give you a huge fps increase.
when games properly support it they work wonders and really give you all they have.
BUT don't forget a few things.
sli isn't something that's good going forward, nvidia have dropped 2 and 3 way sli support nearly, and crossfire/sli support is being handed over to game devs in dx12 nearly, meaning to get decent support, or any hope of vram stacking, your relying on the game devs to want to pay someone to sit there and code it in, for 1% of their playerbase.
think their really gonna care about that?