I have raced two 125 on my raptor. At the time I had a 12 tooth on the front and a white bros.-e. I lose time after time to the one guy and smoked the other we were in loose sand/grave. I spun to much. One time we were riding down a dirt road I was wide open and a 125 went right by me. His bike was stock as far as I know.

 

I would have to say the 125 would win by just a little bit.I have a YZ250 and have ridden a banshee and my STOCK 250 will eat STOCK banshees like their going out of style.So if a raptor is about the same as a banshee ACCELERATION wise then i will say that a 125 will barely beat a raptor.
Just my opinion.