well, i don't own an E9X M3 yet. But purchasing used cars previously, I would much rather have the higher mileage one. Why? Well, you can drive it, see if there is any flaws, look at service records, take it to a Mechanic, have him do a fast diagnostic. Plus, look at the bright side, you are saving money, and the engine is ready for some serious driving
.
GL with your quest.