I regularly go 5-7k miles with Dino oils with no ill effects. I still don't see a reason to switch to synthetic unless you can find it for a price that allows you to get more miles per dollar than dino oils. My worry about the very large intervals used by AMSoil is that they use the same additives that are used in conventional oils. I suppose if I was going to keep my car until I had 250-300k miles, and knew that from the beginning, their may be some merit to Synthetic. I was privy to results from one of the "taxi cab" tests that showed conventional oils with 10k mile oil changes in a taxi cab showed measurable, but negligible wear after 200k miles, and noticeable differences in tolerances at 450k miles.
3k mile oil changes are a thing of the past.
