I got this from the hotrod.com website ( Hot Rod Magazine and Hot Rod TV). This is the test they ran on the TV show....
To see the difference between mineral-based and synthetic fluids, we enlisted the help of Scott Crouse’s ’65 Mercury Comet. With a hot 347, World Class T5 manual transmission, and 4.11 geared 9-inch rear axle, it’s a rolling torture chamber for vital fluids. First we made a series of runs on the Westech Performance Superflow chassis dyno with 20W50 in the crankcase, Dexron III in the gearbox, and 75W90 gear oil in the TracLoc differential; the result was 408.3 horsepower and 405.1 lb-ft of torque. Then we drained the petro-chemicals and replaced them with man-made hydrocarbons from Royal Purple: 7 quarts of 20W50 synthetic engine oil, 6 quarts of Max ATF, and 2½ quarts of Max Gear 75W90. After a 5-mile jaunt to get everything up to the same temperature as the baseline test, we let it rip. The monitor read 418.4 hp and 411.2 lb-ft of torque, a gain of 10.1 hp and 6.1 lb-ft just by switching to synthetics: an impressive tribute to the reduced coefficient of friction. We’ve seen similar improvements on the engine dyno, and have noted reduced wear through the use of synthetics. They’re a bunch more expensive, but in our opinion, they’re worth it for cars you care about. For your $200 Pinto, stick with the 99-cent stuff.
