Loris Gubian won the European 125cc Championship on one... is that good enough for you?
http://www.todotrial.com/ttactual/pruebas/...sy125f-kits.htm
For sure he's talented, but it proves that the bike can be very capable. After all it was developed by some talented guys including Mick Andrews... see:
http://www.todotrial.com/ttactual/competic...sdt2003dia4.htm
[i have the 163 and had the 125 before that]
JohnS