I run different brands front to rear on both Xs right now, but when I pressure up I make sure the center height of the wheels is the same on the front and the back wheels even if that means deviating from the ideal inflation pressure by a couple of psi.

The worst difference I have seen though is less than 1/4" and that does not really translate in to >3" circumference. To get >3" difference you would need over a 1/2" off on the rolling radius....... Generally tires don't vary that much between brands but it is worth checking when you mount new tires that they all have the same radius.