Sparks are indeed dependant on the size (in uF) of the caps, charge level of the caps, and the voltage used.
When connecting the two connectors together, you get a bigger spark if you do it slowly. As the connectors get really close, the spark will jump. If you can do it fast enough, there will be much less of a spark. Deans are probably the hardest to do this with because you have to make two connections at the same time and can sometimes not get them lined up quite right intitially. Bullet connectors are easier since you make one connection and then the other.
As the page linked above says, do NOT use a no-spark resistor on any of the Mamba ESCs. That is straight from Mr Castillo himself. Although, as long as the switch is "off", I still don't see what the problem would be. If the switch was "on", the motor would immediately try to arm and the rapidly fluctuating voltage could possibly cause issues. But, I'm not gonna argue with the engineer after all.
