Don't bother with 6700K. 5930K only if you plan on using multi-GPU or M.2 NVMe. Which leaves you with 5820K. It's a damn fine CPU. I guess all of them clock to 4.5 GHz easily. Anything beyond this depends on the batch. 6 core at 4.5 GHz ain't bad at all.
Though, AMD Zen is really close now I think, would you be willing to wait or are you too eager to upgrade like I was back in autumn 2015 ?
I'm itching to upgrade, but I'm fine waiting a bit, I would be ok, getting the monitors, and being content with that for a while, and maybe spending what I would spend now on the entire upgrade of the core components cpu, ram, mobo, m.2 drive, etc... on a 2nd 980 ti hybrid, I'd have to change my case or mount the 2nd hybrids radiator on the window of my current case. I really want better monitors right now. and that's looking like quite a hefty investment if I get decent sized g-sync monitors.
how long until Zen comes out? I feel like I made the right descision going with x58 way back in 2011. But tbqh, I have the exact same CPU I did when I built this system, and it's been a beast of a machine thus far, I mean hitting 4.2 stable on a 2.8 cpu is really good in my book, I was only hoping for a 4ghz overclock! This was the 1st intel system I'd ever built, and I don't miss AMD one bit, I did re-purpose my old AMD gaming rig x6400(now phenom 9950) original crosshair Mobo, to my media rig which houses all my plex content. I also see that AMD GPU's have less issues with different resolution monitors like My described set up above.
IDK, like I said, the main focus for me is performance, and keeping performance high even when multi tasking. If I'm being honest I've been leaning toward the 5930, because of the extra lanes, more established market etc... but I hear skylake has better single threaded performance and that the multitasking difference is nil, unless I'm encoding video 90% of the time, which I am not.