For context, here is the link to your last post here:
https://felinediabetes.com/FDMB/threads/new-member-asking-for-help-with-dosing.240865/
Did you ever get a chance to talk to your vet about testing for the secondary conditions (acromegaly and insulin auto antibodies) that could be the reason your cat needs a larger dose? There are treatments for acromegaly if that is what he has.
As far as dosing goes, I would now switch to 1 unit increases. Another thing you may want to watch for, is if the Lantus seems to be stinging Kitty Boy. Lantus has an acid base that can sting some cats at higher doses. Look for signs of grumpiness at the shot, walking away. Levemir is a good solution if that is the case. It has a similar action to Lantus, with the onset and nadir being a couple hours later.