2000 V-10 in 35 ft MH. Mobil 1 at 10/20, later changed to 5/20 by Ford instructions. Had the Amsoil dual filter system (standard filter plus a large bypass filter)installed at 6k miles. Thereafter changed regular filter every 7500 miles and bypass filter at 25,000 miles. Each regular filter change a sample was sent to lab for analysis. Lab would return a recommendation to change oil between 35,000 and 45,000 miles. At 130,000 miles had to pull heads due to spit plug. No measurable wear. Had valves polished and the reassembled engine compression tested like new.
The bypass filter is what makes the long extended oil changes possible. It has a very fine screen (.5 micron if I remember correctly) and oil cannot flow through it fast enough to lube the engine, but Amsoil claims that all oil will make it's way through it within 5 minutes.
My experience indicates that the optimum oil change procedure would be filter change at 10k and oil change at 20k. I do not have the bypass filter on my 2014 V-10, but based on my past experience with Mobil 1, and no way to change filters, I use 15k miles as my oil change goal. Anything less than 10k on full synthetic oil is a waste of good oil.