OP from Maine, getting help from guys in California, which is cool. But will the Maine rider suck all that year round dust and use full throttle often through mile long sand washes and rat races over to the next mt range? Maine riding to me would seem a lot easier on the motor ?
In theory the slipper piston short skirts in the modern short stroke long rod motors "should" have less thrust against the bores and give decent service life. They do in autos and some other applications (streetbikes, 4 cycle snowmobiles etc.) with the same engine geometry and metallurgy as these dirtbikes. The difference IMO is dust, and oil capacity/heat/cleanliness. Deal with those factors and you can extend it's life.
I earned respect for yamaha's wr400 years ago when I met a girl riding one on the Alcan highway, She had ridden from southern Mexico to Alaska and was on her way home. Her only fail was from a cracked subframe which was repair welded with a coat hanger and a car battery and was still holding when I met her.