it will go about 190mph(with a viper pouling it) but for real i got a 110 and the cc is just like 6 mor cc in the real cc mark i say 37 34 top speed 110 plus you got the weight of starter, battery

 

45 is reasonable on a good stretch of road I think.

 

but on a good streach of road the gears are winding so loud i guess if you want the rpm winding so high you can blow your motor you could reach 45 but the 250sx is only buildt to do mid 55`s and that my firend is 2 times the cc than the 125 (the motor has 112 cc on 125m
)

 

I have a 125m 1984 and in perfect coondition i took it to the raidar runs i got 47mph... so just to let u guys kno