Hi , i’m getting similiar fps as you. But with steam vr ss 150% and ingame 85%. For me turning vives motion smoothing to on(wich is in 120hz mode very good) and set it to 120hz was the big deal. I couldnt believe that too but it was much better as in 90hz.
Using a rtx 3080 ,i9 9900k ,32 gb ram.
I think Steam Vr isn’t really optimized for msfs right now .