in a sep I've been anything from 500ft to 12,000ft, in a twin with o2 I've been up to 18,000ft, tonnes of fun that.
in a pressured twin turboprop (a P180II) I've been up to 40,000ft.
I fly the optimum flight profile for the trip based on a number of factors.
but I've also been as low as 20ft over water as well.
Fats