Walter:  I understand the theory and am confident you have many Ada test runs to quote.  I am however a curmudgeon test pilot who had been fooled by well meaning engineers for years and like to see FLIGHT data when ever possible.  There are many ways to effect egt in flight and most are easier than putting in new pistons.  Additionally most of the flight conditions I have seen posted here by TSIO-550-8.5 flyers have had LOP fuel flows nearer 19gph than 7.5 to achieve 200ish KIAS so that is a curiosity.  Lastly you also point out that the higher CR engines have retarded timing, and of course lower boost--so it is more than just a piston change and flight experience is worth reviewing.  paul