Even AMD isn't daring to say that they can beat the Intel chips on a single-threaded basis, they said something to the effect that they're a little less thread performance and a chunk less instructions-per-clock.
On the other hand, the 7700k can't really be overclocked in the S4; there's currently no heatsink/fan combo good enough to overclock it to ~5ghz without thermally throttling. It is a 91w TDP at stock, and would exceed that as soon as you overvolt it.
The 65w TDP of Ryzen could theoretically give overall better gaming performance in this case, but few games benefit from 4-8 cores as they do from high single-thread performance. I'd still urge to wait for the review embargo to be lifted on Ryzen before planning your build around it; I own an RX 480 GPU and they straight up lied about the TDP performance on that, as we've seen it can exceed it's TDP without overclocking, and at launch was exceeding the PCIE spec until they did an emergency firmware patch to fix that.
All-in-all AMD can be an excellent value, but performance-to-watt, which is the true limiting factor in cases like this, is still lagging behind Intel/NVidia even with the new process node. I'm rooting to see some real competition, and I'd go all-AMD if I were building another rig in a larger case like the Thermaltake Core V1, but in a case like this where every watt is a challenge to the power supply and cooling systems, Kaby Lake / GTX 10-series is the way to maximize the performance-per-watt.
