any time two pieces of hardware have to work together there can be some loss in performance, as what can happen with sli. the other thing to consider is any other programs you may be using, as some may not like sli, or can only use one video card. if you need that much power, you may want to consider the new gtx 980 ti 6gb.
For Premiere, I'd give my vote to the single GTX 980. While multiple GPUs are supported for exports and renders, only a single GPU can be used for playback and other real-time features.
On another note, the 900 series cards are working great for the latest Premiere Pro versions (latest CC subscription versions). However, if you are using an older CS version an earlier series GTX card may be a safer bet for compatibility reasons.
Using two video cards can only be considered if:
- The PSU has enough power (think 1000+ W).
- The motherboard and chipset have sufficient (32+) PCIe3.0 lanes free.
- The CPU is at least an i7-5690X overclocked to 4.5 GHz, or
- Preferably a dual Xeon E5-2687v3 or better.
- Memory is 64+ GB.
If these conditions are not met, the use of two video cards is a pretty sure way to waste money. SLI is not advised. See Tweakers Page - What video card to use?
You would not profit from extra VRAM when you have two cards. It is not a matter of A + A. It is still handled internally by PR as only 1 A.
CS only supports a single video card.
You actually don't get any additional usable VRAM when you link two GPUs in SLI. In fact, two identical GPUs with 4GB of VRAM in SLI will still give you only 4GB of total usable VRAM. This is because the other 4GB merely serves as a duplicate of the first 4GB.
In addition, the GTX 970 is not a true 4GB card. This is because memory access is split into 3.5GB and 512MB portions, where the first 3.5GB runs at 196 GB/second and the remaining 512MB runs at only 28 GB/second. Thus, it should not have been labeled as a 4GB card per se, but rather a "3.5 + 0.5 GB" card.
Thanks everyone. I'm running 32gb ram and that's the max on my motherboard. I thought that using 2 would give me 8gb of vram, but if it doesn't I won't waste my time. GTX 980 it is.
Only, I got a lot of good info here, I don't know what to mark as the correct answer!