Stephen,
There were many versions of Mosquito bombers.
The first, the B.Mk IV, topped out at 380mph at 21,000ft or so and carried four 500lb bombs internally. Powered by two Merlin 21s it suffered a severe performance hit when modified to carry the 'cookie'.
The first Mosquito bomber designed to carry the 'cookie' was the B.Mk XVI, powered by counter rotating Merlin 76/77 engines it had a top speed of 416mph at 27,000ft.
Thrila,
The Mosquito in AH has Merlin 25s at +18lbs boost (all Merlin 25s ran at +18lbs boost or higher).
The problem it has re due to the flame dampers which have no effect in AH other than to make it 10-15mph slower and the CoG bug that will be addressed when it is redone. Hopefully the dampers can be removed too as Mossie 6s used in daylight ops, which is all that we have in AH, did not have them.