Stainless steel is more difficult to cut, roll and weld than cold rolled steel.  Back purge welding is required when welding stainless or the pipe will crack in the welds.  I know how much time it takes for us to make a HPR 19 with patterns.   Looking at your craftsmanship I think that I can see at least 25 to 40 hours of passion on your good looking project.

Stainless steel does not transfer heat as quickly or does not store as much heat as cold rolled steel.  These two facts will make a stainless steel pipe of the same dimensions and thickness as a steel pipe, come up to temperature a little quicker and will shift the power and torque peaks to a slightly higher RPM.