Power for CG Extra 300
It is not the size of the engine, but how you use the throttle that counts. I have seen them with Webra 1.20's in them. Flew great, but the owners didn't use full power except to climb.
Most I have seem have had a .91 in them. An OS .91FX handles the plane well.
It would seem to me that a more appropriate question would be, "How much trouble am I going to have balancing the plane with a heavy OS 1.08?"
The 1.08 is a good engine, but heavy. If you want power-to-weight, get the .91 with a Performance Specialties or Jett muffler.