as i read the OP, the max speed with goods is 85% (wich is with horses and wich i get, but i have more troops than horses though)
if this is not the case, chadz ought to edit the OP, period.
someone test this pls:
you need 2 troop, 3 horses and 1 good (changed the numbers a bit, just to be 100% sure).
if you don't get the speed bonus of 1,3 or 1,8 then the current OP is true.
if you do get the speed bonus, then the OP should be edited.