With six bikes you have enough time between runs to charge two bikes at a time.
For the NE 24hr race I put together a diesel generator, 8500w continuous. In theory, if each Rapid charger was at full output, 3300 watts, my gen could only handle two chargers, same with the EU6500/7000. In reality, the chargers don't reach their full output on 1.5.1. I'm almost certain we could have run three Rapid chargers on my generator, given that all three chargers would be at different stages of the charge cycle. Unfortunately we didn't think of it at the time and our breakout panel could only accommodate two chargers.