My take on it is this...
In Single threaded stuff 7700k is going to be the better option, for anything that scales remotely with more threads, then the Zen chip is probably going to be the better option. Should we move towards more thread utilisation becoming common practice then the Zen is the winner hands down, no questions asked, it seems AMD's SMT is actually better than Intels HT, from the leaks, although they are leaks and not real solid evidence until officially unveiled and benched etc, but theres a lot of leaks pointing in the same direction so make your own mind up there.
Another thing to consider is what hardware are you running with your CPU, if your gaming where your GPU bound then CPU is going to be pretty irrelevant, either chip will suit you fine, common sense here is to pick the cheapest chip to suit your needs, in this case i feel Zen is the clear winner as not only cheaper but you gain more cores at the same time, so double win here.
End of the day, a 7700k @ 5ghz is going to be a good gaming CPU, nice minimums etc, you have to ask yourself if your happy with slightly less performance but twice the amount of cores for the same or less money.
I think anyone that just wants the absolute best single threaded score will go with 7700k, anyone thats on a budget of some kind and wants an all round PC will go with Ryzen, especially if the prices are to be believed, you can pretty much build a top end Ryzen rig for the cost of Intels highest end i7 (6950x) or even close to the cost of the 6900k.
If moneys no object then your probably better spending it with Intel to eek out the absolute best of the best performance in all areas, if you go Zen your going to probably get 90% of the single threaded performance and 120% of the Multithreaded performance but at a massively reduced price.
Thats my take on it.
Personally for me? my 4770k is going to my kids, im going 1800X for my personal rig, Single threaded will be around the same level i reckon, but i will gain double the amount of cores and threads which gives me a bit more future proofing, DDR4, m.2 etc as well.