Alternatively, it should be possible to write a Lua script to help conducting test flights and record all needed data (plus a small tool to compute the values needed for PFPX from those data sets). I'm currently checking feasibility in respect to the time I personally have to not only come up with such a script but also perform all required flights (even with some degree of automation that's still quite time consuming). The Challenger isn't alone. It's just one more aircraft addon that has no or only inaccurate performance data in PFPX (my last purchases, iniBuilds A310 and Felis B742 have exactly the same issue), so I feel like (even when HotStart provides us with more detailed performance data) that's a reoccurring and quite annoying issue with most addons, so it would be good if there was some general (although time-consuming) solution.
It's also probably best to wait for a few patches before starting such data collection as any tweak or bugfix to engine performance, FMS or autopilot behaviour may to some degree affect the collected data. The initial release probably isn't the best candidate to collect data from.
While I have a lot of ideas I am missing the time to implement all of them (even in best case conducting the flights alone would probably take several days to complete). So do not take this as a promise that I will come up with something usable, at least not in the near future. After all, I still want to fly and enjoy the plane. Please let me know if you are aware of any previous (successful?) attempt to collect data from X-Plane this way or have a better idea.
Edit: I've checked it and it seems to be feasible, even with the Challenger. It may even be possible to almost completely automate "piloting" the aircraft (although it would be very helpful to be able to trigger IRU realignment via a command as it's easy to knock out the INS by repositioning the aircraft). I still can't promise when (or if at all) I could have something ready, though.