Thanks all.
I didn't think about the extra weight added with a bigger gearbox so probably with a lighter engine but heavier gearbox the weight difference would be little.
Peter-RB
It make sense what you're saying about the spare parts and reliability.
the beater
When I went to the Robinson factory I actually remember them saying that Robinson chose that engine cos it had longer life-limited parts than others, so you're right.
r88
In regard to the tip speed I was actually referring to fixed-wing aircrafts, cos I know the propeller is mounted directly to the engine with no gearbox so the rpms are limited by the speed of the blades..