I belive the PML is 3 qts over the 4x4 pan, is also finned aluminum, you have a mag drain plug and an extra Boss to install a temp gauge.
Is not for everyone, works for me, my tranny temps rarely exceed 130.
I don't tow but if I did, with as pricy and sensitive as the 5R55Es are, would want all the protection I could get, plus the ability to monitor what is going on in real time.JMO
Do not think the 4x4 pan is anywhere near two qts over the 4x2, maybe two pints.
Is just a deeper sump.