GTX 970 or an R9 390 for a 3 monitor gaming rig w/ heavy game mods?

I'm a single-monitor 1080p gamer, and chose the 970 STRIX mostly because of its overclocking capabilities. I was able to really crank the thing to 1533MHz for the core and 8000MHz (2000MHz) for the memory, which thus far has put it above stock 980 models while running at about 60C in FurMark. That's at about a 150% power target (BIOS edit). That is undoubtedly the best supplied cooling performance I have ever seen on any GPU I have ever bought. Ever.

However, something like Minecraft with shaders and a 256x256 texture pack uses all, yes ALL of my VRAM very quickly. Assassin's Creed: Unity runs great, but also uses all of the VRAM very quickly, which prevents me from using TXAA without crippling performance. Yes, at 1920x1080.

So if you have the power supply for it, I would totally recommend the 8GB 390 over the 970. The extra RAM and ROPs will help rip through the extra pixels. And if you have a real beast of a PSU, you could pop another one in there in the future after prices drop. The extra VRAM will be glorious in CrossFire.

(I have a tendency of giggling when people SLI a couple of 970's. Basically what you have is a Titan X with <4GB of VRAM)

^^ i dont see the problem there im planning to sil 970s for the oculus rift as well:/
If extra 6gb vram is not worth it over the 980ti to the titan x why is the extra 2 worth it over the 970?
(Aside from the performance increase as thats obviously worth it but 2 970 has similar performace to a 980 ti while costing less)

"If extra 6gb vram is not worth it over the 980ti to the titan x why is the extra 2 worth it over the 970?"

That's a good question. But it has a lot to do with what settings require what kind of horsepower, and how this compares to how much VRAM those settings use as well.

Another way to think about it is this:

Most systems overall will use up most of 4GB of system RAM quite easily, right? But to use 6GB or 8GB of RAM, you have to be doing some heavier-duty stuff, not just simply web-browsing and text editing. More like gaming. So in gaming, video editing, or decompression, you would see a major performance difference between 4GB and 8GB. Thus, it would be worth the extra RAM. This is about like going from 2GB to 4GB of VRAM in current games.

Imagine this system had something like a Core i5. Pretty reasonable to pair an i5 with 6 or 8GB or RAM, right? Now imagine you upgrade to an 8c/16t Haswell-E i7. Nice big upgrade in horsepower, right? Except that you never made any RAM upgrades, so you are still only running 4GB or 6GB, for instance. In most tasks that use a lot of CPU horsepower, you won't be able to see all that performance, because you would run out of RAM long before you run out of CPU power.

This is about like 2 970's in SLI. By the time you are playing a game that can bring 2 GTX 970's to their knees, like 4K gaming with AA on newer titles, you are well past using all that memory, so all that horsepower simply goes to waste because it's sitting around waiting for memory to be exchanged. That is, if 1 GTX 970 is already starting to slow down from RAM issues, adding a second card won't help with much. However, I can see its use in Oculus, like you say, or if you are using a 144Hz monitor, so you would simply run at lower settings to shoot for high frame rates.

But if you are running Shadow of Mordor maxed out, and are experiencing slowdowns due to the VRAM being used up, you aren't going to see any benefit in getting a second card. Then you will just have TWO cards that are running out of memory. Remember, 2 4GB cards in SLI is still only 4GB of VRAM. You don't gain buffer size.

On the other hand, this much GPU power paired with 6GB of vram would make quite a difference. Now you have that extra breathing room for those extra settings, because now you have enough.

Now, if you are talking about the extra 6GB of vram you get on a Titan X, you already had enough VRAM in the first place, so doubling the size won't gain you any performance. The Titan X's framebuffer size was chosen mainly for compute functionality. By the time you are using all that memory, you would have to be running something like three 5k monitors in surround. And at that point the Titan X would be too slow to handle it.

Basically, if you are going to run an SLI system optimally, it would need to have about 50% more memory than one card would realistically use. If the R9 390's weren't so power-hungry, they would be perfect for this application. But the 970's are already using all of their memory. The the main use for two would be to draw things at the SAME settings at TWICE the speed, which is why it would make sense for a 1080 or 1440 monitor at 120+Hz.

Also, the Titan X isn't worth it because it is, like, double the price for a couple percentage points over the 980Ti. 12GB would make sense if it had a 1024-bit memory bus and 8,000-10,000 CUDA cores.

And then DX12 comes out and suddenly all of this changes.

Thank you Jonathanese for explainig to me
I wont go for sli i will upgrade to the next titan (not the x but the pascal or volta one and than buy an oculus)
Im runing on a 1440x900 sceen so im usually far from running out of vram except for some games (shadow of mordor gta 5)
I still think the card is perfect for the time being but i will want to see what a new card will be able to pull off