I'll wade in, here, too. I'm an Amsoil dealer. Not for profit, I don't hawk the stuff. I buy the license every year because it allows me to buy at wholesale for myself and friends. The savings outweighs the license fees, and I get a check at the end of the year for "commission". The benefit of synthetics is they are much less prone to oil failures like viscosity and thermal breakdowns. The key with high end synthetics is to keep them clean. High end is Royal Purple, Amsoil, Lucas, etc. There are others, too. I think Mobile is a great product. Mobile synthetic is the best, by far, of the commercial off-the-shelf oils, but is not as durable as the above.
I run Amsoil in my Dodge with the Cummins Diesel, wife's Ford Escape, family's ski boat, and the Speedmaster. I've used it in previous bikes as well. I change the oil in everything- yes everything- once a YEAR. I ran oil analysis on the Dodge for three years at 5k miles, 10k, 15k, 20k, 22k, and 25k. At 20k, it was always still good to go. At 25k it was still good, but was showing signs of high particulate contamination. I do have dual filters on it, but it also has bigger injectors, stacked fuel and programmers, and a bigger turbo- all of which add carbon and soot to the oil.
So- oil changes once a year, oil filters twice a year.
I'll throw out a couple others as well. My biggest concerns with conventional oils are heat, contamination, and oil base compound. Several of the big name conventional oils are paraffin based. Yes that is paraffin as in wax. Not good for colder climates and tend to gum up if not changed often in any climate.
All this said, Mobile is great. Change it every 3-5k with a new filter. Buy good filters.
