For gaming there has been little reason to upgrade in over a decade; even my old 920/960/980X systems are plenty for 1080p/1440p gaming; heck even my i5 750 can still handle modern games @1080 with a 1050Ti.For gaming at 1440p or better right now it seems academic whether you have a $500 10900k or a stock $175 Ryzen 3600. Just 10 percent between them. Presumably if you're at 1080p with such a high end GPU like the 2080Ti it's all about the frames, but we all know that configuration is a small niche across PC users. 1440p or better is where it's at now and the bottom end of where we'll all be in another 2 years.
For productivity surely you're going to go with the 3900x for circa $400, not least because you also know you can just drop a 3950x in as an upgrade later, or something even faster from Zen 3.
That's it really. If my budget was this level I would plump for a 3900x on a quality board, and then see what 16 core Zen 3 goodness I can plop in there in a year or so for a simple tangible upgrade.