I have owned all three.
Most Torque by far goes to the Sirio/C6
Best run time goes to the Sirio
Longevity goes to OS Speed
If you are comparing for a buggy, I would personally look at the EVO IV STi over the CL7b STi. The CL7b STi is more a torque motor and does not have the top end that the EVO IV has. I switched from the OS Speed which is a great motor to the EVO IV and I get a lot better fuel mileage out of the Sirio. My speeds were great motor though. I personally like the power band of the EVO IV a little better than the Speed. It has a little more bottom end but still very smooth.