No reason to use the discharge mode unless you want to take a full pack down to storage voltage

Your packs should be at a resting voltage of 3.7v or so before charging, meaning your LVC would be set at 3.4 - 3.5v

A 1c charge rate for a 4200mah pack would be 4.2 amps and should take 60 minutes or so from empty

Fast charge should only be used if you are in a hurry, otherwise you should be balance charging it

Cheers