Yes four-strokes do turn bigger props but the Saito 125 seems to prefer a 15 x 8 or a 16 x 6 prop rather than the normal 16 x 8 for a 120 but if you can get someone to tune it properly then go for it. The OS .91 FX is a long stroke engine and it turns the same props as the Saito 125 at similar revs. One very good point about the Saito is how quiet it is even compared to an OS 1.20 it has a duller sound which can make you think it is not tuned correctly and you may feel you need to lean it out more, don't, Saito's tend to run at a slighty richer setting than other four-stokes, just listen for the revs to increase as you richen the high end needle slighty.