the ones I've seen the wheels aren't driven, instead a chain that goes around
the pipe also go on a driven sprocket so it both holds the cutter on the pipe and drives it, so the wheels could just be big bearings
I guess you could use a vfd and a gear motor, but it is probably overkill
and 5hp sounds crazy how fast do you need to go?
how about something real simple for a start, cannibalize an accu drill replace the trigger with a potmeter and an on switch