I'm capable of running 10 with settings turned down on a 6700k with a single 980 TI. The setup listed above would be capable of that, running a second card will mean being able to turn those graphic sliders up. As for the 5820k vs the 6700k for 10 boxing, I really couldn't say. I'm sure it would run it, but I don't know what the exact difference would be. For a single game like Witcher 3 for example, the 6700k will beat the 5820k assuming ram, video card setup, and settings are the same. I'm sure there's a point where more cores will mean less than available core clocks, I'm just not entirely sure where that point is in a boxing situation. Mirai might be able to shed some more light on that, as it's the root I think of one of the biggest questions we have when talking "minimums" or "recommended" builds for boxing.

Either way, I've decided myself to try tag teaming raids with other boxer(s) in the future. Ten works, but man does it hurt the wallet.