Having been involved in fleet maintenance during my career, I'd remark on a couple things. Using the science of oil sampling, A filter does not clean the oil, it is only a suspended particulate trap.
Oil's life is determined by acid/ph balance, corrosive chemicals suspended in the oil created by condensation, cold starts and oxidation, and silicates from intake air (dust). Never change an air filter because it makes you feel virtuous. More silicates are introduced into the engine during filter changes than any other time. A typical highway service paper pleated, impregnated air filter doesn't begin to reach peak filtration until the 'filter minder' shows about 1/3rd restriction. SI engines (gasoline) usually are well within limits on oil contamination at 15 or 20,000 miles. Diesel engines can go much longer, almost indefinitely, when subjected to routine sampling. Eventually, diesel particulate load becomes a problem, and the oil needs to be changed, or in the case of industrial/marine units the oil will be centrifuged to reduce particulates in suspension. Most diesel fleets now are using fuel consumption formulae to determine oil changes after setting the standard with sampling. We overdo it to a ridiculous degree. But, this is not to start an argument, I'm merely pointing out what the industry standard is...you do what makes you happy.
