I think one of the points people are trying to say here is that "future proof" isn't really a thing in workstation tech anymore. There was a day when you bought a computer for 10 years+, then 5 years+, then 3 years was a good target, then 2. At least here in Canada the CRA now allows you to write off a "workstation" in 1 tax year (not true for "servers" or "infrastructure" which get amortized over multiple years).
If this is a business for you, I'd ask, will you break even or profit with this purchase in 1 year's earnings? If a high spec machine allows you to save hours of a precious editors time (saving "salary" costs), release quicker (be first on YouTube or social), or other competitive advantages, then you may justify this as a worthy investment. But if not, you can probably get away with 1/2 the budget and still tackle the same projects. You'll need to crunch your own business numbers to decide. But I wouldn't aim for "future proof". I'd aim for the budget that makes sense in the next 12 months to maybe 24 months. Assume you will replace this machine or upgrade or complement it with new IT purchases in 12-30 months after purchase. I'm not even 12 months later, and the 2060 has gone from "quite good" to "getting old".
Everyone around me buying 30-series cards...
A "consumer desktop" cpu instead of the Xeon will get you higher single core clockspeeds, but will in some/most cases lose the ECC RAM support. I'm not sure how much ECC RAM benefits Davinci Resolve...
But personally for hobby YouTube use I DIY'd my own video editing workstation with:
- Core i9-10900k (10+ months ago, technology moves fast) which will idle around 4.2 Ghz and turbo to 5 Ghz plus, 10 cores total, 20 threads.
- Paired that with an RTX2060 (mid level card, "high end" for most "home users", but maybe minimal for "pro users").
- 64Gb 3200Mhz ram
- 2x m.2 nvme drives
and the machine runs quite well with Davinci Resolve!
This machine renders my 1080p videos in 1/3 of actual video length (so 21 minute video would render in 7 minutes in resolve). And was well under $2000 CAD (<$1500 USD). You can go higher, and may want to for 4k (you said "occasional 4k", mostly HD), but just to illustrate the point that a consumer desktop can do that job if that's the appropriate budget for your operations.
Only you can crunch the ROI numbers by knowing what your income potential is vs costs.
P.S. In the last month or so I've already seen announcements for 30-series cards with 20GB VRAM! Insane.