I think that they got the same power untuned, and on both cilinder you could drive a lot if you maintain them good. I don't know if you have any further plans with tuning etc?
Or get yourself a Metrakit SP2 cylinder kit, it is more powerful than MHR replica cylinder kit (my previous kit), and yet its also very reliable and its nikasil plating is very good.
on the scootercenter catolog disc it gives the mhr rep power output as up to 14 ps and the manston rep as up to 13 ps....both a slight bit optimistic i think.i seen a video of a manston rep tuned and its power output was amazing!it looked like a full manston or team speed!...on the other hand i have fitted a few mhr reps to piaggio engines for people here in ireland and all of them are still running...there are extremely reliable for there power