I wouldn't spend extra for 7600k. Here's why.
1. Games are going to go more multithreaded at some point. Xbox one and PS4 already use 8 core cpus. Stands to reason that when they port they may wish to utilize extra cores on pc as well.
2. Underscoring point above, Coffee lake is releasing soon. Things I've seen indicate they may require new boards. In other words, if that article is true, Kaby is a dead end.
http://www.pcworld.com/article/3217673/computers/intel-images-confirm-6-core-core-i7-desktop-processors-new-motherboard-requirement.html
3. According to the article above, rumor is that i3 will even be quad core. Sounds to me like spending extra for an i5 now which in a few months will only be about as good as an entry level i3.
4. Again, linking to same article, it's clear intel even sees the writing on the wall concerning what I said about multithreaded games and apps. They state that i3 is rumored to go to 4 cores, i5 to 6 cores, i7 to 6 cores hyperthreaded. If intel even sees it, why would one doubt it?
5. 7600k vs 1600. Biggest difference. 7600k today will beat 1600 by about 10-15% give or take on SINGLE threaded apps/games. However, if games start going multithreaded in the next year or so, the tables turn. The Ryzen 1600 is about as fast single threaded as haswell. Put it up against that 7600k in multithreaded apps or multithreaded games, and that 7600k is going to be taken to the woodshed.
If op is open to overclocking, here's a review that sums it up well imo.
http://www.eurogamer.net/articles/digitalfoundry-2017-ryzen-5-1600-1600x-vs-core-i5-7500k-review
Just my opinion here, but the 7600k is a fine chip. No question. But when you look at value for money, if you are already over 100fps in a lot of titles, plus considering he's going to use a 1050ti anyway, number one, the 1600 overall is only an average of say 10% behind in fps. But the op is more than likely playing on a 60hz screen(I do), and he won't see the difference.
As games and apps go towards multithread in the next couple of years, the 7600k is going to show it's age more quickly. In a few months, you might as well call it an i3 when Coffee lake drops. If you wish to see about multithread apps/games, here's a youtube video about Battlefield 1 and multicore cpus.
https://www.youtube.com/watch?v=Y98WlzuG9fw
If you look at the video at 13:50(13 minutes 50 seconds in), he puts up a graph. In that, they show a 6 core should average about 120 fps, and 4 core about 95. If this becomes the trend, yes 7600k will do good for a while, but will age faster imo, and you've paid more for a dead end platform. Whereas you get a ryzen box, if AMD holds true to their promise to support it until 2020, which I think they will, needing to gain market share and good will, as well as they seem to do better at this than intel imo, then in say 2019 you want a new cpu, easy. Drop a new chip into the board, done.
If op wants a little more expandability on the board, here's one for not much more
https://pcpartpicker.com/product/dWL7YJ/asrock-ab350m-pro4-micro-atx-am4-motherboard-ab350m-pro4
Gives the 4 ram slots, actually same board I'm running. Have my 1600 at 3.7ghz on stock cooling. And I haven't even tweaked things a lot yet.
Don't get too overly excited about the higher overclock of the i5. Look at that eurogamer article. Notice when they put the i5 7600k at 4.8ghz, it's still not that far ahead of the 1600 at 3.8ghz in most titles. There are a couple of outliers, but only one or two.
Anyway, ultimately it's not my money to spend, but the 7600k might be more of a dead end than Ryzen. Even if there is a difference, I don't think the op will see it, and it should be made up for as things swing toward multithreading and doing multiple tasks at once.