What do you want to achieve?
If you race your packs until they drop, 10 amp is good enough to take out the last juice. eventually, you can use a 20 amp tray alone, no need for both 20 amps discharge AND 20 amp tray.
If you dont want to take them down to zero volt and you dont race the car till it drop, it might be another story.
So, what do you want, runtime or punch? Long lifetime, or maximum performance regardless of battery life?