This bootstrap approach is highly interesting! It might be somewhat overkill for most cases, but it seems very powerful since it allows to measure one performance curve and derive (from a theoretical underlying) variations in performance data for changed conditions (density altitude, weight, ...).
Although I'm flying a variety of slightly different Cherokees, and the performance would strictly only be valid for the measured plane, I'll try to obtain a some measurements and play around with the spreadsheet.
The only thing that worried me a little bit is the modelling of Vx in the article, which seems to not vary with density altitude (as does the best-glide velocity Vbg, by the way). I guess I'll have to buy the author's book (apparently long out of print) or obtain research papers to learn more about the background.
Thanks for the hint!