The Intel gets a few more frames when gaming compared to the 3900x. But I would suggest the 3800x over the 3900x if your use is primarily for gaming. If you need multi-threaded performance too, then go for the 3900x.
I just upgraded from an I7 960 to the x570 and 3800x. For me, I wanted to be as "future proof" as possible for this build.
With a 2070S, it's a monster and cheaper than the Intel offerings as well.
Good luck on the decision.