yz125s rip..and kx100 r the same..no question whats faster but he will be able to keep up with ya in most areas besides wide open areas...ur friend will probly want a yz125 after about 2 days of ridein his kx

all the quads u listed blow...doesnt matter about top speed...its how fast u get to the next turn

 

the 05 125 are the sh@t..... i have a 01 yz 125 and love it but next year i am getting the yzf250 4 stroke just better power all round just an idea