Hi,
I have flown quite a few P51's including the Dave Platt 81" model, but I have no experience of the 1/6 scale Pica. However, I think the most important thing to check is the amount of washout in the wing. Even a heavily loaded model will be ok with washout ( within reason ). Check that the wing has at least 2degrees washout and fly it with authority. Good luck, a nice looking model by the way.
Cheers,
Merlin man.