I usually fly my Yak with full fuel, but sometimes use 75% or even 50% if the fight is near a friendly field. There is a difference when the aircraft is light vs. heavy. I haven't experimented with draining one tank before the other though (by default it drains the two tanks, left and right wing, evenly).
As for the P-47s other than the N, I don't use the default drain order, assuming I have a choice (75% or 100% internal fuel). The P-47s take main fuel tank hits very easily. So I always drain the main first and leave the aux tank for last. At 75% fuel you only get a splash in the aux tank, but its still worth saving. That aux tank is often the only chance to get home.