Just my opinion-

all sounds great but when you say you can cut off 1 1/2" where does that put your insert at full draw? are you turning the drop away into an overdraw when you cut that much off of them?

418 going 288 for a 29" draw is some great speed. If speed is your only concern I'd leave it alone.
Now if your spine is acting weak ( a 400 spine in your specs, you're borderline) then cutting some length off MIGHT stiffen them up the amount needed to bring them in.

Are the broadheads grouping well at your personall shot distance limit?
If so, leave well enough alone, if not- time to make it so (could be any number of tweaks to make this happen)