I would suspect that most competitors using a .38 rifle, Cowboy or Wild Bunch, are using a velocity of 750-800, at least. This is based on a revolver power factor of 60, and the using the same rounds, the rifle adds 100-150fps, easily. So the POWERR FACTOR may be in the 75-80 range already.
Using a >.40 rifle, with a PF of 150 is a disadvantage, many would agree, as it is easily twice the power factor of the .38's.
I might propose changing the Power Factor for the rifle in Wild Bunch to 80, or any value <100, for any caliber rifle, in any class. This would lessen the advantage of using a .38, and it may allow someone shooting in a "Classic" category to compete with those in an "Open" category.
The 1911 Power Factor would still be 150.
Discussion? Kevlar is on.