Got it working in VR using Pimax 8K and 5K+! The gain is not big, but I would say 5-7fps in average which still is a lot, having in mind this simulator mostly runs in 40-60fps on Pimax with GTX1080Ti and 8700K at 4.9Ghz.
The FOV mode was not working that great. With default value I had a double and mirrored image in the peripheral view. Increasing the FOV number enough to around 74 moved it away from the peripherals but then there was no gain in fps anymore having the FOV mask on, so I disabled it. Anyway, the modded shaders still makes a difference, big thanks for this!
Made a video about this, and overall performance in DCS running on Pimax 8K and 5K+ with my system: