I do not have my sources in near me, but iirc the bulk of the Cromwells had the 6lb'er (British 57mm, which was superior to the US 57mm) main gun. It was fast firing, and had decent enough AP ability to deal with the Pzr III/IV, StG's, and other German medium armor. It needed to be dangerously close to the Pzr V and Tiger tanks to be effective. I do not remember any details on the 6lb'ers HE ability.
Speed of travel and a quick reload for the main gun would be it's two biggest assets in AH. In AH, think of it having the same performance to the Pzr IV in terms of armor, AP ability, reload speed, but with 15mph more travel speed. Oh, and lets not forget the default skin color would be olive drab GREEN instead of neon tan.