In your case, with an RX 590, do NOT buy an expensive x3D processor expecting any improvement. I upgraded from an RX580 (using an original HTC Vive) to an RX 5700xt (and a valve Index) and that's the position you are in. You cannot drive a high pixel density VR headset with a Mid tier GPU from 8 years ago.
Get something that is at least as powerful as that RX 5700xt I had (I now have a 4070 super) and you will be satisfied. It drove my Index at 90hz.
What games do you play in VR? I know you say the outlier frame times were a huge problem for you but it really seems like such a small performance bump to get such a huge perceptual benefit.
Most of my VR time is in Beat Saber -- I'd have occasional, quite distracting frame drops with a 5600X that have completely gone away with a relatively cheap upgrade to a 5700X3D.
I'd personally argue that smoothing out outlier frametimes is not a small performance bump! As an engineer I care a lot about tail latency for services, and I feel like tail latency ends up being even more critical for high-fidelity gaming experiences like VR.
Get something that is at least as powerful as that RX 5700xt I had (I now have a 4070 super) and you will be satisfied. It drove my Index at 90hz.