Nigel
considerable Aerodynamic effect of a pitched up aircraft with Full Flap gives a LOT of Drag...
I'm assuming you aren't referring to all Boeing types? My reading of Various FCTM (apart from the 747-400) tells me that holding the nosewheel off unduely does not help with braking performance, moreover on the type I am most familiar with the 757/767 the FCTM categorically states that the effect of holding the nosewheel off on braking is not significant and therefore not advised.