SU5 changed the CPU to GPU balance quite considerably, with the GPU now being much more the determinant of performance (especially in VR), so the old adage that you should throw the fastest single core CPU at the game no longer applies.
Rather than speculate on whether a CPU upgrade will be worth it or not, first pull up task manager and see what your CPU cores are doing while using FS2020 in various areas you normally fly on the 60 second graph. If no core is maxed out while keeping the view fixed then a CPU upgrade will do very little for you post SU5. Sure, changing the view will see CPU spikes up to 100% and a faster CPU would help with that, but for the most part most performance is experienced in this game with a stationary view.
eg. the highest core load my i9 10850K has with a fixed view is now about 60%, so in theory I could underclock from 4.8 down to 2.88GHz and still get similar performance with one core finally running at 100%.
TBH, your best performance boost in FS2020 VR with a G2 would come from upgrading your video card to a 3080 or better. Yes, your 3070 is no slouch for most games but in FS2020 with a G2, video card performance still reigns supreme even after SU5 and you would get much better performance and render resolution settings with a 3080+ than from the CPU motherboard upgrade you are proposing.