Hi Glen,

do you have an older version of the SP? On the ones sold now they changed the gear, never owned an old version but it seems to make a difference.
I run an 120SP now for 3 seasons, and would not say that there is a difference regarding vibrations compared to other fourstrokes.
They all shake
What I do believe is a difference is the doubled torque, that tries the engine to distort on the bulkhead. If the screws are not tight enough and the engine gets some play things get rough. I had to reinforce the bulkhead, it really has to be rock solid as any weakness will result in movement and loose screws.

Cheers
Andi