For racing I charge my nicd's at 4-5amps and nimh at 6.
For bashing I would suggest nicds 3-4amp and nimh 4-5A
This will help prolong the life of your batteries.
I wouldnt suggest discharging at more than 20a unless you have a pulse discharger such as the DPD or MM CTX-D.
Linear discharging at higher rate ie 30A will cause your batts to get too hot especially if the pack is still near full charge.
Too much heat is the enemy of batteries especially nimh.