The circuit stops at around 10.5k, 11k if I got tailwind or going downhill. The lowboy gets it to 11k and 11.5k with tailwinds/downhill.
I use a 21mm Dell'orto PHBG with a foam TNT filter. 45mm HC head and Airsal piston.
I use the Airsal piston because my TCCD piston gave me issues with raising the cylinder enough to clear the head, it uncovered the intake through the piston windows at BDC losing a lot of power and fuel that way. The Airsal piston has the 4 lil holes model instead of the 2 bigger windows, and the holes sit a lil higher than the windows in the TCCD piston.