Amisol does make a difference in my TC450 dirt bike. Seems to run cooler or at the very least overheat less frequently. I change it every 100 miles, same with the dual sport. It's only 1 quart and only takes 5 minutes,far faster and cheaper than rebuilding a 4 stroke.

Trucks are a different story.
All my 4x4's have gotten cheap 10W40 and a stock filter 4 times a year. Never bothered trying the synthetic for the trucks but guess I might if I ever bought a brand new one.
The Toyota 22R and Jeep inline 6 don't seem to have any ill effects running generic oil.

As for the 5000 mile+ oil change I don't get it. You'll still get 5000 miles worth of crap in your oil wether its still the correct viscosity or not. Why would you want to keep dirty oil in your engine for any longer than usual?

If the synthetic oil came out nice and clean at 5K I'd be sold. Until then I still think standard oil every 3months is the ticket for my rigs.
One of my friends swears by Mobil 1 in his Jeep,only changes it twice a year. Maybe we'll pull the oil pans one of these days and have a look to see which engine really is cleaner.