Jonathan; thanks. What you describe is really how my thinking is. I think the lighter weight and shorter lens is probably the way to go for me.

Rich; I think it wouldn't matter which lens or which combination you use as your results should be about the same, as long as you use the same lens at the same distance and same subject with each camera. Here is my suspicion of what we would find in such a test; of course at higher ISO's the 1D X will prevail but you have to get to 6400 or more. At the ISO's we believe the 1D IV was always acceptable the 1D IV will resolve and be better than the 1D X crop. A win for the 1D X here makes the long lens crop argument meaningless.