Yeah, I meant to say "and the other display is connected via HDMI, which limits it to a hard 30FPS max regardless of how much video card I have."

With my 780 and only a single client, I was able to run Ultra and *usually* stay at 60 FPS, though when there was a ton of action, that would drop down to 45ish FPS.

Thanks for the feedback, MiRai - good things to think about and know. I hadn't really been considering the impact of a 4k stream on performance - I've got to think about how to handle that, and it will take some experimentation.

I also got similar feedback about waiting for the next gen cards - namely that we have no idea what will happen and anything really performant will likely be the Titan equivalent, and I can always resell 2x 970s if something compelling comes along. So, with that said... Yesterday I went and got my parts and here's what I built:

Corsair 540 Air case (thing is freaking huge, but the airflow is delicious and cable management is a non-issue)
ASRock X99 Extreme 4 mobo
i7-5820k CPU (6 cores, 28 PCIe lanes vs. 16 - lets me run 1 gpu at 16 lanes, 1 at 8) + better cooler
32GB Corsair Ballistix Elite RAM
2x ASUS Strix 970 GTX
EVGA SuperNova 1000 watt PS
1TB Samsung EVO 850 SSD
Windows 10 Pro

Once I finished putting it together and sorting out a few configuration snafus, it's been running like a dream. I haven't set the cards up as SLI. I'm still trying a few tweaks to performance, but if I'm just running a single instance, it stays at 60fps in ultra settings, and when 5boxing, I lower the settings for my main screen a bit (good to high) and get 60fps consistently and the followers all stay capped at 30fps. I'm hopeful with a few more performance tweaks I'll be able to get my main screen back to ultra - my guess is that there's a CPU bottleneck since the GPU is entirely divorced.

Still haven't messed around with streaming, but that's next.