@ what fungus said your power loss is more with the P channel then the N channel.
Only if you select the incorrect P channel mosfet.
My choice:
http://www.fairchildsemi.com/ds/FQ/FQP47P06.pdf
Rds = 0.026 Ohms @ -10v Vgs
Your choice:
Rds = 0.035 Ohms @ 10v Vgs
Both require 10v gate to operate at that Rds, so you really need a driver for both.