Normally you should be able to get the mount cheaply

Since you would go 9700k max OC or 3700x with hopefully highest clock I guess you should get a good motherboard with nice VRMs etc.
I've just watched a few videos about x470 vs x570 and z390 boards.
x470 is the way to go if you don't need the absolute best nvme pci-e ssd speed. PCI-E 4.0 won't be needed anytime soon. Even PCI-E 3.0 is barely needed and only for rF2 apparently but not really proven...
x470 doesn't have a damn cooler, is cheaper, will continue to be supported and the 3700x clocks just as fine on them.
Here are the winner boards:
Z390:
Gigabyte Aorus Master
Gigabyte Aorus Elite (cheaper and still good VRMs etc)
x470:
AsRock Taichi (ultimate only got the extra LAN thingy).
The AsRock apparently has the best VRMs, same level as the most expensive Gigabytes but costs a lot less, has a debug code display.
There's also the z390 Taichi which also is advertised with the 12 phase VRMs but I didn't see it in the videos.
And it's not cheaper than the aorus ones with this chipset...
Hope that gives you some starting point
Thank you. This is actually the much needed piece of information here. There're no good VR-specific tests out yet and I had no idea whether the lack of cores or lack of per-core performance was the reason for my current system struggling in VR because it clearly lacks both. I absolutely agree that even 5-10% could be a "make it or break it" case for VR, seen that myself already where adding just a few more opponents to the grid can send me into permanent reprojection mode because the system can't do consistent 11.1 ms frame times anymore
To make it a bit more clear:
Assetto Corsa could be labeled a "2.5 thread application".
When you look into the running threads via "process explorer", you'll see when a thread runs into its limit. For my 4c/8t i7 2600k it's 12.5%.
AC has one thread running between 11-12.5% if I unlock my fps and another thread running between 10-12%.
And a third one a lot lower... And a lot of tiny threads without real load.
So the real test would be to run Cinebench with 2 and then 3 threads and compare results but absolutely nobody is doing it... Actually I did with some friends of mine.
In VR, you get a higher CPU load because of VR being VR. But it's not like you'd get a "VR thread", no, the VR load is just added to the already limiting 11-12.5% thread.
Windows is pretty good at spreading single threaded loads across all cores (basically one core per splitsecond running at 100%, then the next one that already cached a little bit of data).
It can increase the overall CPU load quite a lot so a 2.5 thread application will almost max out a 4 core CPU!
(which is why the 9600k is basically fine with 6 cores. The 9700k only adds a few fps due to the better spreading with the same IPC and clock).
Here's my custom Cinebench table across the amount of threads. It's a mix of tests from the internet and runs from friends and myself. I estimated and filled in the missing data from the data I had available and also calculated the results going from my own CPU being able to run 50 fps for direct comparison:
And for 3 threads (closest to most simracing titles right now, going from 60 fps):
i7 2600k @ 4.4 GHz: 60
i5 3570k @ 4.2 GHz: 58
i7 8700k @ 4.8 GHz: 85
i7 4790k @ 4.5 GHz: 70
Ryzen 2700x OC (whatever was possible with the AMD boosting): 74
i3 8350k @ 4.9 GHz: 83
i9 9900k @ 4.7 GHz: 84
However if you take AC:Odyssey, which runs on 7 main threads basically, the results would be:
i7 2600k @ 4.4 GHz: 60
i5 3570k @ 4.2 GHz: 45
i7 8700k @ 4.8 GHz: 103
i7 4790k @ 4.5 GHz: 68
Ryzen 2700x OC (whatever was possible with the AMD boosting): 99
i3 8350k @ 4.9 GHz: 66
i9 9900k @ 4.7 GHz: 111
Here is the big graph: