The PHEV will be somewhat heavier than the HEVs; however, I anticipate achieving a genuine 55-60 mpg on motorways without charging, provided one adheres to the speed limit, accelerates smoothly, and anticipates deceleration by coasting instead of braking (and, for clarification, I acknowledge that braking also recharges the traction battery, but coasting does as well).
I would not cancel my purchase; these vehicles are exceptional.