I've been charging my race packs at 6.5 amps for a while now with no bad side effects yet. My practice pack(s) only get charged at 5 amps (the night before) and the 3300 MiNh packs in my Nitro Starter box get charged at 4 amps.
Start at 5 amps and go up if you need more voltage to keep up. If your batteries seem excessively hot after charging, them lower the threshold slightly.
MATCHED packs can handle the higher amp charge rates, where as NON-matched packs can fail at rates higher than 4-5 amps. Not passed along info from xzy website, but my actual experiences from the last few years of racing. Take it all in, experiment, and use what works best for you. Most of all, go have fun.
