I found it interesting that none of the software I have selected so far is
more specific on a PA-28 than to be a "generic" pa-28. I fly the Cherokee
140, which does have a different performance than a Cherokee 180. Minor
gripe, I guess, but a little annoying because the POH for the Cherokee
(1969) really sucks.

Most decent packages allow you to edit the aircraft performance profiles.
Jeppesen's FlightStar/FlightMap allows extensive modifications and you can
swap data files with other users.