there is no point making a faster spooling secondary, its controlled by a vacumn chamber in the engine bay if u want it to spool earlier simply modfy the crossoverpoint,
as for changing sets over, i have recently done this from a vf13/14?(i forget entirely) to b4 set up so in the ranges of v18/19? anyways it boosts alot better and higher too with the secondary running at a solid 17psi vs 14psi with a drop to 9
changes are minimal but its no longer noisy : )