I am considering buying a 520EXC. I have mostly owned two stroke motorcross bikes but have on occasions ridden the odd four stroke (Husabergs, Yamaha etc). I ride in natural terrain areas. Top speed doesn't concen me but hard acceleration from point to point does. What concerns me is the weight factor and reliability. Has anybody out there recently moved from 2 to 4 strokes and what was the result. Thanks.