if I recall correctly, you can sit on the window sill in No. 10's cab. That makes a big difference as you can't sit on the sill in 9. Also if you're on the tall side you have to stoop slightly to stick your head out the window so you have to be either inside or out.
And, the brake wheel in 9 is in the way, and now the vacuum brake stand is there on the engineer's side.