It seems like most of this issue would arise with the engine cold, rather than at full operating temperature with the benefit of the warm water circulating in the manifold. As a theoretical excercise, total power produced seems like it would be down as a result of a warm(er) air intake temperature compared to an unheated manifold. Just as an aside, I have the heating cicuit on my Weber and manifold combo on my 220. The heating circuit seems like it would help prevent carb icing as well. How about another choke cable running over to a 1/4 turn ball valve that you could turn on and off? (Yep, something else to forget!)