The best deal is to keep Peking drake with Muscovy hens. They produce a giant mule which cannot reproduce but they do get large in record time. The meat is not as sweet as the pure Muscovy but if u are breading to sell then u may have a good business going there...
If you breed Pekin drake to Muscovy hen then all drakes will be as large as Muscovy drake but all females will be small like Muscovy female.
On the other hand if you breed Muscovy drake to pekin female then both drakes and ducks will be as large as Muscovy drake.