I've let it fall to no less than 40, my commute is 40 miles back and forth anyways, and I know that on our old Explorer we always let it fall into empty, and the fuel pump gave out in four years. Whether they were related, I don't know, but I don't wanna risk getting stranded, especially when it gets to the low teens around here lol.
Avant Garde M310 Hyper Black. ST2 Recaros. Downforce USA Front Lip. KW V1 Coilovers