Wait another week or so and there will be benchmarks available for Ryzen. An 8 core, 16 thread Ryzen 1700 will almost certainly have far better performance in heavily multi-threaded applications than a 4 core, 4 thread i5-7600. However, most games don't yet make use of that many threads, so it's possible that you might not see a big difference in gaming performance, at least not with today's games. If you plan on keeping the CPU for a number of years though, having more cores might give it more longevity, as more games and applications begin to make use of them.
If you're not in a super-big hurry to build a system right now, there should also be mid-range Ryzen processors coming out within the next few months or so, which will likely include 6 core, 12 thread chips for a price closer to what what the i5-7600 currently costs.