I think 70 - 80 is ideal for 35mm, but an 80 for Medium Format is more like a 50 in 35mm.... So I've heard..

By that rationale, the 105 should be something like a 75 in 35mm, which is pretty good... And with a F3.5, I can get that nice shallow DOF. The 135mm for the Mamiya, bumps it to a F4.5...