I've read an article that stated that the engine wear rate actually decreases, up to a certain point, as the engine oil is used for some time. This may sound crazy, but could there be some advantage to draining/replacing 1/3 of the capacity of the engine at 1/3 the mileage interval? For instance, if the capcity is six quarts and the oil is normally changed at 7500 miles, you would drain and replace two quarts every 2500 miles.