Well.....to be honest, I'm none the wiser! And quite frankly, I'm beginning to wonder, whether any of them make a busting lot of difference, as the fact is, myself, and everyone with a seven that I personally know, changes the oil every 3K or so regardless. So it's hardly in there long enough to deteriorate anyway.
I notice that high performance engines are mentioned a couple of times, which I also find quite amusing. The cars may be reasonably high performance, but the engines certainly aren't! The K series (which I have) must be a 25 year old design, originally out of a Rover 200? And even the current Duratech must now be getting long in the tooth, but neither of them were intended for high performance vehicles, were they! It's hardly F1 territory.
So, I suppose, the question is, does it really matter, as long as we are using the recommended type/rating?
Oz.