[Michael C Henry]

Electricity should be thought of as a circle.If it comes from the battery it has to return. Anything and everything in the circuit has an effect.The smaller cable on the return,ground,has a limiting effect. you can tell if the smaller cable is a problem by the heat and magnitic feild created when in use. The cables should all be cool.The starter also has a limiting factor, making it work. If the current didn't do any work ,resistance, you'd have a big surge and end up in a melt down.The bigger the cable the less resistance.If you use the same size neg as pos and they are ample size the starter and battery become the limiting factors. If you were to keep upsizing the cables eventually you will see less and less of a gain. Point of deminishing returns.