You can run over the circuit breaker amperage for small periods of time, the circuit breakers are thermally controled:
http://team358.org/files/electrical/snap-action_vb3.pdf
http://team358.org/files/electrical/...ec%20Sheet.pdf
Also I wouldn't recommend running mini cims on the drivetrain unless you are geared very slow, around 5-7 feet per second. That would basically max out those motors potential with ~150 pound robot.
Here's a suggestion, what about using Banebot motors and/or Andymark motors for the shooter, and cims on the drivetrain? You may be surprised with the power you can get out of Banebots and Andymark motors, and the torque when they are geared properly. There is also a weight savings going in that direction. 6 shoot cims seems over powered for a 3 pound ball, I don't think they would break a sweat, but I don't know what your setup is either.