9zap here is a rule you could follow.

Nicad batteries Maximum Charge rate = (x2) it's current = 6Amps
NiMH batteries Maximum Charge Rate = (x1) it's current = 3Amps

Remember to condition your new batteries for like 3 cycles at C/10 charge rates first to get the maximum capacity.

C/10 = 1/10 of your current.

By the way you could charge at higher rates but remember this that higher the current you use = lesser battery life span.

Personally I charge my RC car batteries at C rates which is 3amps for the 3000mah battery after the initial conditioning.

I am not sure nor know if you get more punch and longer run time by charging it at higher rates because I thought mostly the charging rates and voltage are already established when they are first made and conditioned by the factory or companies who sells the cells. That is why you see the figures on those single cell batteries with all those numbers. I thought by charging them at the higher rates people do on their chargers, it just fills the capacity up faster.

I am not completely sure, only nominally sure so I would maybe ask some battery experts. If you need more info go look up the Batteries/Chargers forums on this RC Universe. They give great advice without all this clutter. They are friendly and seem helpful. Most of em I see are RC Airplane/RC helicopter users which are very picky about how they charge their batteries and their maintenance.