I have three Mitsubishi, two Pontiac, and one Ford vehicle. I use Mobil one exclusively and change the oil and filter every 20,000 whether it needs it or not. One Mitsu, one Pontiac, and the Ford have over a quarter million miles with no excess oil consumption. One of the other two Mitsu's and the other Pontiac are close to that. I've had only one front seal leak on a Mitsu and have done some valve cover gaskets over the years on them, usually near the 200,000 mark. I have used my bore scope on the higher milage engines through the spark plug hole and still have very defined and visible crosshatch in the cylinders and no ridge at the top. I figured out a long time ago that the savings from changing every twenty instead of three thousand miles would more than pay for an engine or short block if the extended oil drain interval every killed one.
Also, keep in mind that pao based oils can handle the extended use much better than hydrocracked and that the better the additive package / detergents, the quicker it gets dark. If it stays clean looking, it's not suspending the contaminates.
Oh, I didn't mention that when you remove my oil caps or remove a valve cover, you could eat off of the top of the head. When the oil runs off of the metal surface, it's as clean as a new part is out of the box. Since I going on about everything else, let me mention that all of my savings are actually paying for brakes and transmissions. I drive the heck out of them. Green means go and I pretty well floor it. When the light turns red, I don't touch brakes until I'm right on it. But I never have engine trouble. I just thought I would let you know in case you wanted to run it longer. It won't hurt a thing.