well, my idea for that one was the following: first the missile launches and make as much speed as possible. at the same time, it is moving towards the target area, towards great heights, but not yet at the end of the atmosphere. most speed is made in this stage. then the missile drops the booster, and advances towards the target. the booster itself is only made for great range and speed. the main missile differs only in the nose: the ABM and the long range air launched versions are the only ones which have active seekers, so they can take out targets even out of range from the launch unit's (guidance) radar
you think that is doable of could I better just use one booster for the long range and ABM versions?
The idea is that the missile on the ABM version is probably not going to have the same diameter as the rest of the missiles. You want to take the booster for the long range ship launched version and make a wider missile body for the ABM version.
As for active seakers, The US is moving to make the long range ship launched missile have an active seeker with the SM-6.