I have mine geared for about 260 odd km/h top speed (according to gearingcommander.com). Fastest I ever got was 252, but that was with the mother of all tailwinds directly down the straight (kinda terrifying actually hey Binksy :P ). Normally only get about 240ish top speed. Seems to work pretty well around the track as far as gear changes go. I think 15/46 will get your model R6 close to what mine is.