The C-Series have a finned can for better cooling and a screw on end bell vs pressed. The C-Series stay together, the std. versions have been known to "spill their guts" on the track after a hard wreck or landing. That can be overcome by using the RC-Monster heat sink/motor clamp for $24.
It is best not to use the BEC on the ESC. It add more heat to the ESC. Basically the ESC has to take your 14v batteries and drop that voltage to 6 volts for the servos, receiver, etc. It does so by converting/burning off the excess voltage which heats up the esc. That is why the UBEC is hugely popular. Less heat....happier and better performing ESC!
For speeds, plug your info into Brians Calculator. It depends on batteries, truck weight, gearing, etc.
Link:
http://www.scriptasylum.com/rc_speed.html