Considering a DRZ400SM for my 37 mile commute to work, about 1/4 gravel the rest two lane blacktop thru the cornfields. Max normal speed would be 65 mph. How long should it last before overhaul. I am a 50 plus rider, current mount 07 RMZ 250 for motocross, prior 12 were rm250's. Was bike mechanical during college so the maintainance is not an issue just want to be sure it makes economic sense and gives my 944 turboS some time off. thanks.