This is a very controversial topic and one that will likely not be put to rest until some fanatic is Uganda conducts a double-triple-blind test.
Interestingly enough, changing the cable on my HE-5LEs from the OFC to the SPC (silver-plated copper) did yield noticeable results. The differences have been well-documented and it's one of those things that contradicts my beliefs. Are aliens coming? I sure hope so.