I'm building a gaming rig and I've been flip-flopping on the GPU, per usual. I haven't payed much attention to the developing technology over the past few years, so I've been reading around playing catch-up. Anyhow, I've pretty much settled on the ASUS R9 280X for several reasons. It's fast as fug, good price erformance ratio, and it has 3GB of vram. To me, the 3GB is a big deal because, in the next year or two, I'd like to either switch from 1080 to 1440 or greater resolution or get a 3-monitor setup, and I understand that those resolutions will utilize the increased vram from the typical 2gb in most mid-range cards. My question is, if I get a GTX 760 w/2GB and decide to run it SLI in the future, will two of those cards still only be effectively utilizing 2GB of vram or with they have a cumulative effect and act as 4GB? Also, if I was to get one card with 2GB, would I then be able to run it SLI with another card of the same make and model but a 4GB edition? I ask because I'm considering instead getting a MSI GTX 760 OC 2GB because it's cheaper, I prefer nvidia, and I think that, at the present, it will be sufficient for my needs. I just want to know whether that would provide me with the opportunity to SLI and run 3 monitors in the future.
Also, something I forgot to ask....my mobo is an ASUS M5A97 R2.0. It has two PCI-E 2 (x16, x4). What does the "(x16, x4)" part mean? I gather that that refers to how efficiently two cards can function in SLI/Xfire?