250cc per fork
i have a ktm 85sx and a kx 85 small wheel. i am a midgit but i can ride them. i am twelve. this should help. a kx 85 big wheel is an awesome bike. although if he or she is small it will be too big. a ktm big wheel is expensive but is worth it. it is still quiet big. these are some seat heights kx 85 = 840mm ktm 85 sx = 850mm rm 85L = 850mm cr 85 = 860mm yz 85 = 840mm but all these are ajustable my bros 14 and he rides a ktm 85sx big wheel. he is 170cm tall.
Not too fast
i have a ktm 85sx 08 small wheel. i weigh about 35kg and my brother clocked me in at 65 mph. it all depends on your weight track and your bike. but why the hell would you want to do over 100 kmh on a dirtbike.
Depends on the bike.
63mph
Not as fast as a GSX-R1000
about 90 mph
108.5mph
around 80
A ktm 65sx will go about 43 but with fmf pipes it will go close to 50
Very Slow! KTM's are NOT worth the money AT ALL!!