The individual guns would dictate the size of groups you would get. Neither cartridge is all that inherently more accurate than the other.
Just a thought. The recoil of the more powerful round is likely to make group size larger on that one. Even if you are tolerant. I have 44 Mag and 454 Casull Ruger Super Redhawks and get smaller groups with the 44. vs 454, but 44 vs 45 Colt (loaded hot to 44 Mag levels) the groups are about equal.
In short, my opinion is that at equal power levels, the groups will be equal if all other things are equal. But the differences in individual guns' inherent accuracy will overshadow any difference the ammo makes.