I have the 9450 in myhyper, the sevo the 9451 replaces
there are great

9405 not as fast or as strong, but decent
9206 stronger but almost twice as slow and use only 4.8 volts systems
9205 fast but not strong enough for steering and also use only with 4.8volt systems

if you were looking for non digital the 9402 is the 9451's egual
I'd hold out and order the 9451's