I agree with Tattoo on the hours to check. The 450X is a pretty tough machine. I look after 2 450x's in Australia for 2 enduro racers, and the conditions here are tough. Our dust is like Baja silt!! That's the number one valve destroyer and we are on the original valves after a full season of HARD riding, and 1 top end.
The new KLX450s are good, but not as good in the fuel mileage, due to a smaller tank. They also boil over quicker because the radiators are the same ones off the KX450. Hard to do though. This bike is more race orientated than the CRF, harder suspension and narrower. The CRF will be more comfortable over long and rough rides.
Hope this helps