i know the 2007 yz250 is a 2 stroke and the 2007 250f is a 4 stroke but why is the 250 more expensive then the 250F? i currently have a 2001 yz125 and im thinking about upgrading to a 2007 250 but then i saw the 4stroke 250f and im trying to figure this out? whats the differences and the best bike?