Personally I would want the heaviest slug I could get away with, also the widest, and of course taking precision and BC as top priorities as well. Why??? it's because using a larger caliber will do a few things that would help.
#1 the smallest spinners would be easier to clip on the edge(well all of them would).
#2 it is easier to see where the projectile lands in the dirt or on steel. This affords faster corrections needed for wind and drop.
#3 they have spinners which must be hit at the appropriate time to make it go over a full revolution, and you get bonus points depending on how many revolutions it spins.
#4 it'd be cool to see the faces of the 22rf guys after a NRL22 target gets smacked with a slug twice the weight of those 40gr 22rf's
Though everything has trade offs. There will be more air used, more recoil, more expensive to shoot, you might have to wait a little longer for a spinner to settle back down to hit it again, etc. Might even be more negative aspects I haven't thought of that won't be realized until experienced.