Concerned about how long you run your oil? Go to Blackstone Labs (not the fitness supplement company!) and get a free oil sample kit. Send it in and have your oil analyzed complete with a TBN check to see how much "life" was left in it. I did this on a restored car and it was excellent. Research the TBN rating and you may be shocked to learn that even "old" oil has not lost any of its protective qualities. Excellent company.
When I worked for Department of the Army in a maintenance shop we did this. They did a AOAP (oil analysis program). We usually just changed oil filters and kept the old oil if it tested out ok. My question is this. What does this oil analysis cost. I can do a complete oil change on my vehicle (Mobil 1 & Motorcraft filter) for about $25.00 when I get the Mobil oil rebate. Even if the analysis says my oil is good, I would still change the filter. How would these costs compare?