Using Mobil 1 0w-20 may be the best for racing, since the lower-viscosity "20" number means it takes less horsepower to run the oil pump, giving you slightly more horsepower available to drive the wheels! Slight horsepower advantage with the thinner "0w-20" Mobil 1 synthetic, but possibly less engine life. The Mobil 1 "0w-40" would make the engine last longer in racing, but it soaks up more horsepower than the Mobil 1 "0w-20" --- you choose which is more important when racing!
Many racing teams will qualify using a lighter synthetic oil, and actually race using a thicker oil. That is mainly because engine life is not important during the brief qualifying runs. However, during a long race, the engine must hold up, so they lose a little horsepower to the oil pump in exchange for better engine life.
For everyday cars, startup-cranking-wear dominates the engine wear picture. That means that Chevron Delo 400 Synthetic 0W-30 is the best if you live north of Texas, and Mobil 1 0W-30 if you live south of Texas (southern states only).
Why? Almost half your lifetime engine wear occurs during cranking (confirmed by several engineer friends and also by Mobil Oil Company), so a 0W-30 is the right weight to cut wear down. The "0W" part means the oil gets up and gets going to the bearings the fastest during engine cranking at start-up. Therefore, a "0W" is the best. (A "0W-30" can be used where the manufacturer recommends a 5w-30.)
But why Chevron Delo Synthetic 0W-30 for anybody who lives north of Texas? Taking the "Dragnet" approach, "Just-The-Facts", look at the incredible technical spec sheet at
http://bestsyntheticoil.com/dealers...une-17-2003.pdf and notice that Chevron, employing some of the best engineers and having some of the best labs in the world, have come up with a synthetic oil that has a Pour Point of -76 degrees below zero. BEST THERE IS. That low number means that their Delo Synthetic 0W-30 oil resists the bad effects of cool temperatures, indicating that it is going to flow better when the weather is simply below freezing as well. By the way, the Chevron oil's Flash Point is still OK at 419 degrees (any number over 400 is good).
South of Texas (any southern state), its fine to use Mobil 1 0W-30, since its Pour Point is almost as good as Chevron's Delo Synthetic, and Mobil 1 has a slight edge on high temperature Flash Point.
Also, Mobil 1, like Chevron Delo Synthetic, is produced by world-class, well-funded engineers with some of the best labs anywhere. This means Mobil 1 or Chevron synthetic have proper additive packages in addition to having oil that flows at cooler temps and hangs in there at high temps.
Chevron Delo Synthetic 0w-30 may only be available at trucking supply stores. Mobil 1 is available everywhere.
I don't work for Chevron or Mobil. I am an engineer (Mechanical/Aerospace/Computer) and I think you've got to go on the facts without ANY marketing hype.
It may be noted that Chevron sells the Delo Synthetic to trucking fleet managers who they know will see the numbers, so marketing hype is not going to suffice. That might be why Chevron has the best Pour Point while some other more heavily consumer-advertised oils don't.
For higher mileage (more than 75,000 miles) it may be good to go to Mobil 1 0W-40. Again, stick with the "0w", but in this case make the top number "40" to fill the larger clearances in older engines. I'm not completely sure about whether you really have to go to the 0w-40, and if it was me I would stick with the Chevron Delo Synthetic 0w-30 for any car in states north of Texas, and Mobil 1 synthetic 0w-30 for southern states, as in the analysis above, even for older engines.
good luck