Between those two choices the OS 2 stroke would be my choice. I have a Magnum .52 4s in my .40 size Cub, and it doesn't have nearly the power of the 2 stroke .46 it replaced. To get the same power from a 4 stroke, you'd need to be up around a .65 or .70. FWIW, I'm going to suggest having a look at the Thunder Tiger .46 pro. They are essentially copies of the older OS .46 (FX I believe) and are well made. I'd say they are the best value in RC engines on the market today.