aside from changing tires, taking off or adding shims is really easy as you know

the only reason why i said i don't go over 2.5mm was because that's the most i've used. and also, i remember reading XRC a while back and it was about the shimming not to go over 2 or 3 mm which was based on robbie collin's mtx-3 setup tips. i should still have that mag somewhere but it will be pretty tough to find it now but if i do, i'll scan it and post it over here.

next time, if i feel there's a need for more shim in the rear, i'll definitely try more like you suggested