i'm sure zipp makes something stupid light if you are looking to spend your money on that sorta thing.

i agree that getting a road double will find you with a lighter crank than true track cranksets. i agree with looking at the BB weight too. the move has been most recently to external BB's in road cranks, providing a larger (stiffer) and hollow (lighter) axle.

for instance (these are road weights):
DuraAce FC-7800: 761g
DuraAce FC-7701 crank: 599g + DuraAce FC-7703 BB: 211g = 810g