51.1 mph with the gp 460 backed the run with my gps, both speedo and gps read the same. the tanaka 47r will do 46.9 both have x can mufflers with internal baffles, elbows and silicone tubes, that reduced the noise, but still a little on the loud side. No db reading but sounds like aroud 90 db, I fly rc planes and they do a db reading before they let us fly so I have a couple of plane in the 90 db range and the bike is about the same. X can with no baffles no elbows, no silicone tubes is extreemly loud.
I am running a 15 tooth on my gp 460 also, I am pushing 6.0 hp. I have 1500 miles on my belt, but I always peddle 7,8 mph before I start engaging the motor, and I ease in to the gas, and the few times I went for top end 56.3 mph I did not give it full throtle untill I was over 30 mph. I baby it!