AC500 is a great machine. 165 all day every day, 170 out of a perfect example.
AC680 is fantastic machine, well balanced and good load, between 185 and 200 with 600-700kgs load (depending on how you balance it). Not as good range as a 500 with aux tanks though. Biggest downside is that there are only 3 IO720 680s in aus that I'm aware of and CASA is not pleased with any of them.
TS did all Todd's training and knows the Panther and Mojave well. From those that have flown them, the Mojave is as good as a piston gets.
I wouldn't be letting anyone with less than 500me cmd fly any of these; other than the shrike. Even they can be destroyed by the wrong attitude.