Two 2080s in SLI and the graphics quality set to ten and only one card does all the work, makes a lot of heat, and the system still does not tap the second card. Weird.
You can try Direct x 11 and Direct X 11 legacy. SLI does not work with Direct X 12
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Actually, I have two computers. One has two 1080s in SLI and uses DirectX 12 and the system does in fact tap the second card. So I don’t believe the idea that DirectX 12 does not foster SLI–unless that only applies with 2080 cards. And neither DirectX 11 nor DirectX 11 Legacy settings make any difference. Anyhow, thanks for commenting. 
As far as I know Direct X 12 does not support SLI. But it does support Multiple GPU’s . In theory windows under direct X 12 can assign rendering tasks to other GPU’s in the machine without them being in SLI or even the same brand . Its likely that with the 1080’s there is enough load for windows to warrant using the second GPU. but with the 2080 windows does not see the need.
The profiles that make Multiple GPU’s work are written by NVidia. Its also possible they have not done it or do not intend to .
I recalled a tech forum discussion from last summer that I saved in my favorites.
With my two 2080s, and using HWMonitor GPU, Memory, Frame Buffer, Video Engine, Bus Interface on the one card are all at a big fat zeros and only once did “GPU” move (to 17% momentarily) while the other card is spiking up in other areas: GPU to 100%, Memory to 62%, Frame Buffer to 51%, Video Engine to 42% and Bus Interface to 7%. Those zeros seem like such a waste. My two 1080s sport higher numbers across the board for both cards, especially memory (though).
It does, however it requires that NVidia and the developer work together to provide profiles that support it. Because the developer can almost always get better performance using each adapter independently. As such this is rarely done except when NVidia feels there is a benefit to doing so, which is almost never. For MMOs such as WoW this is almost never the case because WoW is inherently CPU not GPU bound. NVidia actually wrote a series of articles on why explict GPU parallelism was better even with the SLI or NVLink Bridge. That said supporting this is quite a bit of work of dubious value at the current moment for WoW. It may come in a 9.x patch at some point but I wouldn’t expect support in 8.x at all.
Jessail touches on the point in my mind. One GTX 2080 is going max the game graphics. The performance is thrown on the CPU. Wow loves it’s single thread.
What do you have installed there Fumbleclutch. AMD falls down single thread - even Threadrippers. A great overall Intel CPU can have middle of the road single thread.
Post 8.1 this is less of an issue, post 8.2 I would say it’s a non-issue for anyone using graphics settings other than DX11_LEGACY. AMD processors are just fine for WoW now regardless of GPU. The issue is more that due to the very nature of MMOs in general and WoW’s engine in particular it will be some time before it becomes GPU constrained on that sort of hardware.
I’ll take a wait and see seat there. Wow has always hammered the CPU - I don’t see that changing much.
I can only go based on observed behavior on my 2700x: which is that the main thread now only holds 80% utilization. As such IPC (Instructions per clock) is less important than it would have been in the past. In general I see one thread at 80% and a few others at about 16-20%.
Yet my 4690K pins one core and my wife’s 9600K pins one core. With the others like you say 15% or so.
We shouldn’t take this thread sideways with debates though. I avoid those - just an old troubleshooter is all I am … haha
Yeah my point was more that WoW doesn’t currently support multi-adapter rendering. That may change but I wouldn’t expect it before 9.x at a minimum.
9980XE (18 cores). I went overboard. But I still love my old machine–built in 2011–with which I then went overboard, too. It has a six core chip (but as above–uses the two cards installed there).
With DirectX 12 came a huge change to SLI and CrossFire, now it is more labeled as multi GPU due to Windows 10 having the ability to mix a Radeon and Geforce in the same system and have the best of both worlds, i would not be surprised if one day WoW supports a Radeon & Geforce in the same system and label it as “Hybrid WoW” or something like that!
While the 9980XE is a monster multi-thread processor. It’s single thread score is similar to a i5 8500. Still a decent single thread score. My opinion is any bottleneck you may have in Wow would be there.
It’s interesting that the Geekbench 4 benchmark doesn’t have any 9980XE scores as of yet. It would be interesting to see what your 9980XE scores there single and multithread. (you may take over the leaderboard multithread) 
(After the benchmark runs a webpage opens with the results. Paste the URL)
I ran one on my 4690K running a 4.5 Ghz overclock.
Another thing to note, most non-LGA 3647 boards and CPUs won’t have enough PCI-e lanes to run both of those cards in PCI-e x16@3.0, usually they’ll fall back to x8@3.0. Thus the bandwidth to each card will be cut in half. This actually matters quite a bit as it means that the ability to texture swap is significantly reduced. To the point that you might actually be better on most motherboards of running single card for now. Games that directly support SLI and have profiles can somewhat get around this because in SLI the memory on the cards is mirrored and thus loading to the primary adapter also loads to the secondary.
Note: the CPU mentioned the 9980XE has 44PCI-e lanes, that said you should check the motherboard manual to figure out how that actually translates to the slots on the board as quite a few of those are probably dedicated to the chipset and NVME drives.
Once hot weather is upon us it will be interesting to see how the system functions. A single AIO water cooled GPU might have been the better way to go. On an aside, the CPU has a combination air/water cooler on it–a Ryujin 360. The case is a view 71 with six Noctua 140s top and front. The top has the rad in a push/pull configuration.
Just to update this thread: It turns out the NVLink wasn’t pushed all the way in and to get it all the way on the cards required a lot of force. Now both cards are working. Problem solved.
Grats on some serious OVERKILL while playing WoW!