Damned if I can see how the Lord mounts are going to change performance.
If t'wer I, I think I'd fly two identical performance climbs - same day, as near as possible same W&CG, use a GPS to cross-check pressure against geopotential altitude, and groundspeed for the same heading and altitude within an hour or so of each other. Record everything readily available (far better and safer, have somebody in the right hand seat do that whilst you concentrate on flying accurately and looking out): so IAS, GPS G/S, GPS Alt, Pressure Alt (make sure QNHs match), VSI, Ts&Ps, RPM, then afterwards total fuel burned. Record that every minute or so, or every 500ft or so through the climb.
Then line up the data and see where the differences are - you should start to get some useful clues. Bung it all in Excel and plot some graphs - and wherever the graphs are significantly different (personally I'd plot everything against altitude, with time another variable - also work out RoC numerically from altitude and time and plot that on the same scale as the VSI reading) you'll find the significant differences.
G