i think mx bikes are just a bunch of compromises from the front tire to the back, with nothing in between being perfect in design. when you lengthen the rod the cylinder has to go up, making the engine taller . ya you can change the wristpin height to compensate for the longer rod but you can only change the pin location so far. not to mention when the pin hieght changes so do alot of other things in the engine. im pretty sure a short engine, low in the chassis is gonna handle better than a tall engine. the 125mm rod was probly the best compromise of keeping the engine short but still working decent in the overall engine package. cr500 rod could easily be put on a 250 crank and i would like the see the results of that engine. not just slap a spacer under the jug but also a well thought out pipe and porting. maybe it would be a failure but still i would like to see what happens