got this 42 rear and the 13t for the front. the combo is AWESOME off and on road... yah you miss the top speed a bit, but this is not a highway bike so i'll live with it. the difference off road is night and day, that front wheel comes up NO problem its a blast. wheelies on the street are just a snap away. ps the rear sprocket is hard to get off.. don't strip them!
I ride lots of off road and found these sprockets to wear real quick. Used the 42T on my rear for 1,500 miles and it was trashed (Stock chain, Honda chain tension specs checked and oiled on the regular). Now using the 48T and will go with the conversion kit to run CRF250R sprockets next order.