I don't think asking for proof is an invalid question. If you send you fluids to Blackstone and they come back with an analysis that says the contaminant levels are low enough to use the factory recommended intervals what is there to gain by changing it more often? I'm sure M did quite a bit of research and testing before setting the standard recommended and CBS intervals.
I'm genuinely curious about your response. I understand wanting the car to be in tip top shape but I think your numbers are seriously getting into the diminishing return area.