To me, I would consider the 2700x the better buy for now. I have seen this proc on sale for $139 and about $20 higher not on sale. With the looming 4xxx series coming if you are willing to have the "lesser" processor for a few months after the release the 3700x will also be on a similar price point, so you will have purchased both for less than the one, now. OR, if the 4xxx are THAT much better, you could get one of those.
Are these US dollars? I've never seen the 2700X going for those prices. The lowest I've seen is around $190 on sale, which is what it currently can be found for. According to PCPartPicker's price history graph, they haven't seen any lower prices than that from the major online retailers they track...
https://pcpartpicker.com/product/bd...core-processor-yd270xbgafbox?history_days=730
Perhaps you're thinking of the 2700 (non-X)? That can currently be found for around $170 on sale, but again, I haven't seen it at prices that low. In any case, the 2700 pretty much needs overclocking if you want to get optimal gaming performance out of it, as its stock multi-core boost clocks are rather low relative to other Ryzen 5 and 7 processors from that generation. Overclocking can give it 2700X-like performance, but you will probably want a better aftermarket cooler for that, at which which point you've paid just as much or more than a 2700X (which comes with a better cooler), and about the same amount as a Ryzen 3600.
So, the real question becomes whether the 2700X or 3600 is the better option around that price point. The 2700X offers an extra 2-cores with 4-threads, but the 3600 offers around 15% better IPC on average, while still having a very capable 6-cores with 12-threads. For lightly to moderately-threaded tasks, which covers the vast majority of today's games and applications, the 3600 will be the faster processor. For the minority of applications that can fully utilize all of a processor's threads, the 2700X can pull a bit ahead.
At least when talking about gaming, in today's games, the extra cores of the 2700X won't make much difference, but the faster per-core performance of the 3600 can, particularly for high-refresh rate gaming. The same goes for general desktop use, where the higher IPC of the 3600 can make performance in most applications a little snappier, but not much will be using the 2700X's extra cores, and I don't expect that to change anytime soon. Those extra cores would probably only be worth considering if you are primarily concerned about performance in some heavily-multithreaded applications that you know will use them, such as CPU-based video encoding software. It's anyone's guess whether the additional cores or higher IPC will make more of a difference in the games coming out five years from now, but I suspect both should still be reasonably capable processors for quite a while, with the 3600 being slightly better at most tasks now. Because of that, I would take a 3600 over a 2700X if they were both priced relatively similar.
Of course, there's also the 3700X, which offers both the extra cores and the higher IPC, but at $130 more than a 3600, I don't feel it's as good of a value for gaming and most other tasks, which again, won't likely be making much use of those extra cores, at least for a while. In a gaming build, that extra $130 would likely make far more of a performance difference if put toward graphics hardware. And by the time games are heavily utilizing those extra cores and threads, presumably some years down the line, I suspect there will be even faster 8-core, 16-thread processors available for around $200.