My somewhat flippant remark has been interpreted correctly for a change...
My BR blue period stock gets the P4 standards applied. Mind, it is handy being a member of a P4 group. Drop in wheels, very few connecting rods, fairly straightforward...
The CLC/LMS/LNER derived stock is in EM. Why? Valve gear in P4 ! Clearances ! I wish to build and not tie myself in knots. I have friends who make exquisite models of steam locomotives in P4 but auld sausage fingers here? Believe me, I have endeavoured and been unsuccessful...
You make your own choices, it's a hobby after all.