I always run my tank from full to "light on" and never experienced a fuel pump failure even in Texas heat. I think the cleanliness of the fuel you're using and staying away from high solvent additives contributes more to fuel pump reliability than not going below a quarter of a tank. I try to use only Shell gasoline.

2002 X5 3.0 265,020 miles
2004 325i 116,500 miles