LOL. Massive is right for Pekins. That's a lot of the reason that they're one of the main ones raised for not living long. Well, that and the light skin that presents well if you're into that sort of thing.
The BO cross sounds very possible with yours based on the way you describe their plumage and now knowing they're a little, just a little, smaller than the end of the standard scale. All the standard scales depend on pure breeding many generations back, so they're not at all dependable with crosses. We had a KC that bonded and mated (a lot) with a Rouen drake, and the progeny turned out much closer to her size than to his.