Re: How long will it take
I'll be sticking with my 3800X system that I built back in April... It's a good little CPU that I've got on a 4.4Ghz all core OC @ 1.23v. So it's nice and cool on the H115i AIO, with fans/pump on the quietest settings it idles 18ºC above ambient and about 20ºC higher than that under heavy loads.
I can't see any reason to upgrade a CPU like that for a couple more years... even if that system had a 3090 in it, I doubt you'd be anywhere close to a CPU bottleneck.