read on wikipedia, that an apcbc round was produced for this, with a higher muzzle velocity. spww2 only has ap at penetration 8 for all versions of this gun, as far as i can tell.
Ordnance QF 75mm
sounds fishy to me.
traced this source though, go to page 7
fire and movement
is there any truth in this? i hate that damn gun and it would be nice if cromwells got some decent firepower