I have the OS .18CVRX(S) on my RC10 GT, same engine different shaft, (pay attention to Dustin) and she screams!
VERY reliable, great torque and starts easy. Even during break in the very first time I tried to start the engine she started in about three or four pulls.
I spent a little more money and got the OS tuned header and pipe and WOW what a difference that made! Big (read BIG) change in response, speed and torque.
Very forgiving in weather differences and came with a couple very good filters.
My vote hands down!