Look at the system holistically.

What are you doing, and where are your current bottlenecks? How long do you plan on keeping your system? Most folks run about 5 years, with 1 mid-lifecycle upgrade.

If you go with the 2080 - then your midlife upgrade will be the both CPU and Motherboard. You can spend an extra $60 or so now on a X570 MB and then your midlife upgrade would only be the CPU. Ebay the 3900X and that should cover about 1/2 of your CPU upgrade. Otherwise, factor in the cost of either an X570 or X670 (Zen 3) motherboard.

The AM4 socket will be supported through Zen 3, so you will have the ability in 15-18 months to move to a Ryzen 4900X CPU. A mid-grade 450 board can't take advantage of everything that the 3900X brings to the table, (i.e. PCIe 4.0 or the ability to address 128Gb of ram), not to mention the goodness that is coming with Zen 3 (another 15% increase in instructions per clock [IPC].

Also look at the amount of ram (3200 is the sweet spot) - Ryzen uses dual channel memory - If you go with 32 (2x16) configuration, you will be tossing ram sticks when you go over 64Gb (And you will go to at least 64). Remember, you have 12 cores - don't want to starve them.