Wow, lots of differing opinions. So, here's what I do and have done.
91 Ford Explorer, sales vehicle towing 5000# trailer.
After initial break in, switched out to Mobil 1 syn and a wix filter and ran 12000 mile changes for over 200,000 miles.
After I sold it, the fella who bought it said he went to check the valves and the covers were shiny enough to see his reflection, and the compression was at spec.
He was a Ford mechanic.
95 Dodge Caravan same deal, after 187000miles still running strong when it sold.
2001 XJ, still running strong, 140,000 miles and 12000 miles change intervals with Mobil 1 or K&N filter.
I've saved money and time running synthetics, I don't buy "Dino" oil.
I have several Motorcycles that get similar treatment, although they go fewer miles because they are either air cooled, or notoriously hard on oil due to shared tranny systems.
Shear is the problem in this case.
I know some fellas on the Mazda forums who will tell you that Mazda Turbo's are REALLY hard on oil, and they ONLY run synthetics.
Mazda recommends 7500 mile changes, and makes NO recommendation for Synthetic.
I know a Mazda Service Manager that claims he replaces a lot of Turbo's.