I know you can get a special dust cover to get a stem really slammed, but what is the minimum recommended amount of spacers to prevent steerer damage on a carbon steerer?

5mm top spacer
40mm stem
5mm spacer
5mm cone spacer

Trying to compare the HT length of a threaded frame to a threadless frame. I know some lugs have a taller head lug for 1 1/8 steerers. Minimum spacers would seem to take up most of the difference between an external cup threadless and the locknut on a threaded headset.