Look, it seems like you're really trying to prove something here, so I'll say this... I'm really happy for you, and Imma let you play at Ultra using DX11 all you want, but from what I can see in your video, it shows that you're completely maxing out your system and it's really struggling to keep the game at a playable framerate.

The recorded stream does not look fluid or smooth, it looks very choppy because your framerates are all over the place (as is expected when running all of your clients on Ultra) -- Your main client is literally bouncing around from 20-60 FPS and there is no fighting or any action happening on screen. When you're directly outside of the entrance/exit of Orgrimmar, and there aren't that many people around (maybe 15 at most?), your main screen is hovering around 20-30 FPS and only goes back up to 60 FPS when they're out of sight or when you're in the tunnel.

There's no doubt in my mind that your GTX 670 has more GPU power (and more video RAM) than my GTX 580, but 1GB of video RAM is 1GB of video RAM across video cards no matter what. After I made my post earlier I went back and re-measured my video RAM out in Pandaria just to double-check myself. At the very minimum, the Ultra preset using DX11 was taking up 800MB of video RAM (no MSAA, just the Ultra preset). I did a fresh login and spun my camera around so that everything in the scene could be fully load into memory -- No moving and no fighting. I measured both DX APIs in this fashion and DX11 used up 400MB more than DX9 did. Here's some math:

800MB x 5 clients = 4,000MB (or 4GB) at the very minimum. In your video, you show you're running at 3.6GB and there's hardly anything going on in your video (low pop inside and outside of Orgrimmar).

400MB x 5 clients = 2,000MB (or 2GB) - This is how much more video RAM is required to run Ultra/DX11 over Ultra/DX9 across 5 clients where I was in Pandaria.

The point of my post was that you tell people you're able to play using Ultra on all of your game clients at once, and while you technically are able to (your clients aren't crashing), I think you'd be crazy to find those framerates as acceptable. I don't think anyone wants their main client to be maxing out at 20 FPS during a big fight whether it's PvE or PvP. So, let me ask you this...

Do you find the performance you displayed in your video acceptable and would you take your 5-man team into a large-scale battleground or into a typical Zerg world PvP situation (e.g. Stormwind takeover) with all of your clients set to Ultra/DX11?

If the answer is 'yes', then feel free to keep telling people you're able to multibox using the Ultra preset across all of your game clients, but I ask that you include what API you're using, what framerates you're getting (be honest!), and what video card you're using.

By the way, your GPU and CPU loads were lower in the Task Manager and GPU-Z because your main client was out of focus and therefore locked at your background framerate with the rest of the clients at 20 FPS.

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Now, here's a little hardware science for everyone...

Note: The screenshots below are from some old Cataclysm tests I had ran. You can completely ignore the FPS in these screenshots because the framerates were all over the place and the numbers you see in the screenshots represent nothing of value.

Exhibit A:
http://i.imgur.com/nOvBz.jpg - CPU 51% // GPU 81% - Ultra Video Preset (No MSAA) (5 Clients @ 1920x1080)

If I was experiencing bad framerates with my setup while multiboxing five clients using the Ultra preset and I was instructed by someone to check my load percentages by running the Task Manager and GPU-Z, I would report back that my CPU was at about 51% load and my GPU was at about 81% load (screenshot provided above). Given those load percentage numbers, my CPU and GPU should still be able to push more FPS than what I'm seeing. So, why would I be getting such bad framerates in game?

Exhibit B:
http://i.imgur.com/YyJjs.jpg - CPU 96% // GPU 94% - High Video Preset (No MSAA) (5 Clients @ 1920x1080)

The answer becomes clear when looking at the same setup with a lower video preset. You can see that my load percentages are visibly higher when using a lower preset. Why?

Reason being, is If you are putting more load on your computer hardware than it can handle you're going to see lower than expected load percentages because your hardware is being overworked and it can't keep up. When this happens, you will see shitty framerates in game that bounce around all over the place when you're not really doing much of anything.