I race with only 1 pack per class and I charge all my packs at 40A irrespective to capacity because that is the max limit my charger can handle and this typically gets my packs charged in roughly 8-10 minutes. Many modern HV packs are designed to be able to handle this abuse, though it will reduce the lifespan of the pack. I can't speak for Reedy Zappers personally, but I know of many racers in my area who also charge these packs at 40A without issue. Most of the budget brand packs I have used in the past would tend to last around 6 months when charged at 20A which was the limit of the charger I had at that time. I am running Trinity White Carbon packs now and they last over a year (without significant loss of IR) when regularly charged at 40A.
If you do not have an IR meter to check the health of your cells, then I wouldn't recommend charging above 1C:
Which charger is the best?