The tests I've seen -

In the same weight - (10w30)
Amsoil is probably the best base stock. They don't use as many additives as some others. It doesn't really burn off easy though. This indicates the base stock is actually thicker, but still flows thin.
Royal Purple, Red Line are not far behind in burn point. However, they both contain large quantities of zinc, which is a kick-ass pressure barrier. It's why Royal Purple claims it will "micro-polish" the crank, rather than score it. Neither has super high quantities of cleaners.
After that, Castrol, Valvoline, Mobil-1, and most other major brand synthetics. They still have a VERY high burn point compared with a standard oil. (About 150 degrees higher, which is significant, in that AMSOIL being one of the best burns at less than 500...) These have modern formulations for SAE specs. They have high detergent contents, low zinc levels, and are very good oils as well. You can add the shelf Royal Purple (non-race-version) to this group, except the burn point is higher.

By comparison, GTX being one of the best dino oils (Rotella and Valvoline being the other high end oils) the dino oils have burn points around 275-325 degrees. They physically cannot have as much additive of any sort, due to the impurities found in them naturally. They are also much thinner at the same weight, they cannot use the same levels of thermal expansion agents, which means they wear out faster.
It's that "sheer" problem, that causes turbo cars to prefer synthetic. The tight clearances and high heat levels inside the turbo cause the oil to sheer from the expanders much more quickly.
IF you run a regular oil in a turbo car, it's highly recommended you change it VERY often!

Basically, in every possible way, Synthetic oils are better, discounting price.....
Hope that sheds some light on it for some of you.