I don’t think the 10900K has an integrated GPU, so Rack should be using the RTX3090 automatically, but maybe I am wrong.
I had massive problems with my UR22 (mk I - but should be the same driver). Have you installed the Steinberg/Yamaha-Driver? Then use ASIO. If that does not work, try a different USB-Port (The UR22 does not like USB3 and PCIe Gen4 is also not working) I had to buy a seperate PCIe-USB-Card to get it to work properly.
But first thing to do is to check this: Solving DPC Latency Issues | Sweetwater as Eurikon already mentioned.
When I said “essentially identical,” I meant they’re both as fast as I would expect. And for me, totally useable. But I don’t make patches with 700 modules in them. That wouldn’t work so well on my lowly computer.
But within the limitations of my old hardware, and me being happy enough with a 512 samples buffer, my machine does OK with Rack. There is something weird going on with the OP’s computer.
Ok after several tries I found what’s wrong. If using a 1080p monitor everything is smooth. If using 2k or 4k monitors all become sluggish. Maybe vcv is not optimized for these two resolutions. Running on lower desktop resolution and all is blazing fast.
I’m on a 4k screen and had troubles with the Intel onboard GPU.
Then I got a NVIDIA GeForce GT 710 for about 50 bucks and all problems are gone. Windows TaskManager says 92% GPU load for 3D (whatever that means, I’m not a GPU expert). The Rack runs at 30 Hz framerate.
It is not normal for a reasonable decent video card to have sluggish performance with VCV. I’m sure your gaming computer has decent graphics, so this does not sound normal. Are the drivers fully updated? Anything unusual in the VCV log file?