Marty, Group II+ gear oils with a borate additive package (potassium triborate) will generally outperform most full syn oils with a conventional Sulfur/Phosphorous additive package.
Think Caltex (Texaco/Chevron) Delo diff fluids and Penrite's competition 85W-110 diff oil.
They really are very good.
The only downside is they don't tolerate water well, emulsification and then seal degradation occurs.
There is a smaller, boutique blender out of the US that focuses on industrial lubrication and uses a proprietory additive package in their gear oils that outperform most all full syn fluids with their mineral (Group II+) fluids. Their full syn fluids are of course a step above in terms of oxidation resistance and therefore life.
What tends to happen is that some blenders use the better syn base stocks with an additive package that isn't as robust as they'd use in a good mineral or semi-syn oil to reduce costs and present their product at a better price point.
The lines these days are blurred between mineral and synthetic oils, and the most important part of the oil isn't the base oils any more but the synergy between the additive package and base oils. The clichéd whole is greater than the sum of its parts.
A clever blender can make a semi-syn fluid perform as well as an average full syn oil. About the only time a full syn fluid will outperform a really good semi-synthetic is outright life, yet the oils specced and licensed to meet ACEA E6/E9 and most Euro truck engine manufacturers (think 100,000km oil change intervals) are Group III based, severely hydrocracked mineral oils.
Even though they are allowed to be called synthetic here and the US, in Europe they are technically semi-synthetic due to their refining process. They are derived from mineral oil.
For most uses most people don't need a POE dominant based engine oil, or even a PAO based oil, they'll never stress the engine enough to make use of the esters inherent advantages, or need to use the PAO's ability to flow at a -30* start in winter, and think of all those trucks pounding out 1,000,000km before needing a rebuild and doing it on 30,000km oil changes with mineral oils.
Would they get better results using a 10W-40 and 100,000km OCI's?
Maybe, but it comes down to cost/benefit.
Which one would I use? Probably the syn oil. [bigwhistle]
