Bench rest is often seen as a 22 calibre discipline where you are allowed to shoot 177 and have your pellet holes gauged out to 22. It can make sense to shoot it in 22 in the first place if you have a suitable rig.
Not so easy if you are using basically a FT rig, which many do.
My rig is an AR20 with a T35 scope, and the best pellet for me is the Exact Express 7.9 grain.
Just out of interest, in our region we can shoot either 177 or 22 but we do have to stick with the one calibre for a competition of ten rounds. There is no requirement to stay with the same ammo though.