If you plan on using it on highways and ride it over distances, you need the more endurance oriented engine. That would be the engine on the 625SCX or 640 LC4. In my opinion, the EXC models are probably too competition oriented to be the best choice. You basically choose between 20 running hours service intervals, or a few thousand kilometres. The latter being the sensible choice if those 20 hours are not racing or race training. Obviously those bikes are lighter and faster at lo speeds, but you will and must do a lot of maintenance. Check for oil volume. Less than 2 litres is no good for \