No claim to the "guru" title from me. A genetics "guru" might be more useful for your question. Here is observation/opinion on my part: I am sure there is some genetic table that could give you probable out come percentages. I would imagine there would be some of both and some "tweeners". Hope Gary sees this and corrects me if needed. As far as the "physical barriers" to bantam/large fowl copulation........that could easily be overcome by artificial insemination. Just curious, why would you want to do it?
Tim
My very limited knowledge in the area of genetics have come about from first hand trial and error, and reading available literature on topics directly related to projects I am undertaking, or considering. Crossing a large fowl with a bantam does not fall into either category, so sorry, not a lot of help here.
However I can say from first hand observation, that a Old English bantam male (one of my daughters 4H birds), will attempt to cover large fowl hens. While we never tried incubating any eggs to confirm completion of the act, it was not for lack of effort on his part.