RE: Sail sizes + power
Bruce P. gave you a very detailed explanation of the difference between your older Blue Label 410 Super Comp Epoxy mast ( A 410 EPX actually) and the Backbone 400.
According to Bruce the 400 EPX mast has the exact "spot on" bend characteristics, so you will get very similar shaping, but you won't get the panel tension that you will with the significantly stiffer Backbone
Bruce suggests that your 410 EPX mast will work, but it will be better for lightweight sailors (< 150 lbs.) who do not have the weight to load the mast heavily.
The draft won't travel, unless you are heavier and can exert the force to bend the mast more.
Interested sailors can find Bruce P.'s answer on rec. windsurfing
Hope this helps,