If you have no size and weight restrictions, you can design for 50-70 kHz and make life easier for your self
If you have a buck circuit with 100% high side drive then you can have 48Vin & 48Vout but there will be a slight IR drop in the fet.
there are plenty of driver chips for this, with and without level shifting for the high side series pass buck switch
also consider a P channel fet on the high side - easier to drive/level shift in some respects...
good luck...