i don't know about the towing cap. on the 4x2 and 4x4. mine is 4x2 w/ the bigtow pack. and mine is at 9500. payload, at nissanusa.com it has that the 4x2 has a heavier payload. max payload on mine says 1408lbs. i just hauled over 2000lbs in the bed this last monday w/ no problems. the 4x4 does sit higher in the front than the 4x2. here's a link because it has different numbers for the XE, SE, and LE and CrewCab and King Cab.
NissanUSA.com