There is no advantage to having a straight hole which would be the rationale for using a stepped reamer. I think the perception is that a tapered hole like you'll get with a tapered reamer will allow wobble, but the hole is not a load bearing surface. All it does is center the prop on the drive hub. Once the prop is centered and tightened down, the hole could be a half inch wide and would have no effect on how the prop performed because at that point the friction with the drive hub is the only interface between the prop and the plane. I actually ran a prop once a while back that had the hole reamed out too big. It had been reamed for a different engine but was still a good prop. I put it on, eyeballed it center in the hole, and tightened it down. Once the prop nut was torqued, you'd never have known the hole was out of spec because the prop was properly centered and balanced. I ran it until I decided to try a different size and it went back into storage to await its next mission.