Not sure about the values, but I would sure opt for the 42 if I were you. Our first rotary was an R40 and we found it to be a real dog for power. Of course, we didn't know about any Hyper mods back then but it would be interesting to have that combine back and try the mods just to see if we could make her run better. We ran the 40 for 1_2 season before trading up to a late model 50 - huge difference!