a 1C charge rate means you're replacing the full Capacity of the pack in one hour but we don't run our packs to zero remaining capacity, it's more like 25% remaining. so to replace 75% of the pack's capacity at a 1C rate means we're looking at a charge cycle of about 45 minutes.
a 5000 mah pack needs a 5A current to charge at 1S, 10A for 2S, etc, etc, etc, since the 5000 is its Capacity (a 1C charge rate means 1 times its Capacity).
those big chargers charge at high rates only with a pack or two (maybe three) attached. They won't (some might but most won't) charge at high rates when you have six packs attached. Six 5000 mah packs is a combined 30,000 mah equivalent pack for the charger to charge. It would need 300 A to charge at a 1C rate.
My iCharger i306B maxes out at 30A so I can parallel charge a maximum of six 5000mah packs at a rate of 1C. If I were to hook up six 8000 mah packs I'd still only have that 30A max charge current so my rate would be much lower resulting in a longer charge time.
