You sound very GPU limited. I had similar specs to you awhile ago but upgraded to a 4090 and a 13900k. My FPS in VR are in the high 40s with the latest su11 which is a horrible update for performance. I run Dlss and open XR at 200%, everything is smooth and sharp. I used to get in the high 50s with the previous version of the sim.
If you don’t upgrade you arnt going to get more performance even with open XR. This sim isn’t cheap to run well. Oh and 25 FPS isn’t acceptable in VR for me and most others. Especially if you are turning at a high rate of speed. Also don’t run DX 12. It will hurt you in your situation. I personally can’t stand motion reprojection but that could help you a little bit. Worth a try.
Maybe you can find a used 3080 ti. I had that card before I got the 4090 and it gave me pretty good performance in VR. If you can afford to throw some money at, it its worth it. I hope the next update optimizes the sim better.