If your buying an exhaust for long term reliability the fit of the pipe and mounting system used is as important as the stuff it's made from.
I wouldn't use stainless in preference to plain carbon steel.
But surely performance will be your goal or you wouldn't have fitted an RB, so why not see what you can get performance wise that gives the power to suit your riding/gearing/carb.
Stainless Exhaust
i have a sterling stainless exhaust on my 200cc vega i have reworked it to look like a dj so it is solid mount all the way through its rock solid doesnt move at all so havent had any issues with it at all .ive also made some dj copies these are completely solid mount we are not having any trouble with these either so im of the opinion solid mount is the way to go if possible. just my opinion .