I'v been using synths since 1988 (Buick GN) back when all you heard about was Mobil-1, and i was told that was the best available at that time....Since then i have tried a few other brands and so far, here's what i found tested on my Turbo Buick +500HP (same 10w30, AC filter Change every 2K miles)
Mobil -1 3840miles, breakdown, 1 filter,didnt even get to swap another filter.
Castro Syntec 7000miles, breakdown,3 filters
Penzoil
Synthetic 8000 miles, breakdown, after 3 filters,
Amsoil Synthetic 15,000miles, still no breakdown..7 filters later and still running great.....may change by july 06 for B-day...
Well i just know my cars will not leave home without
AMSOIL ...Just like Amex.