40:1
for 2009 KTM 125SX $5998 US
MSRP of the 09 KTM 125 SX is $5998 USD.
63mph
Yes the frames are exact and the 200/125 share the botom end/cases.
You can find that info , as well as a lot more, here: http://motocross.transworld.net/2003/07/09/2004-ktm-125-sx-200-sx-250-sx-and-525-sx/
110mph
The year matters. stick with an 03 crank.
Ktm 125sx
I personally use 32:1 of amsoil and regular unleaded gas for my ktm 125 sx 2003.
KTM recommends Motorex Top Speed 4T15W50 for the 125SX.
A Ktm 125sx is not a good trail bike because sx means super cross so it is a good racing bike it is good for jumps and racing