Following up on Porter's post if I might (but not disputing anything therein),
I thought I'd add that Royal Purple's normal line (not racing oil) is mostly PAO and pretty much in line with the (mostly PAO) Mobil products (who by the way makes the PAO base stock for most other US small market brands including AMSOIL). Motul gets their base stock from Fuchs (any Euro readers of this thread - what can you say about them?). I have no idea about Silkolene base stock source. High ester brands for street use are Motul, Silkolene and Redline, but exclude Mobil 1 and Royal Purple - not sure about Neo and there are many other niche market brands.
My readings indicate that esters can tolerate higher temps than PAO before destructive breakdown of the fluid (actually I "think" it's shearing of the molecules under heat and pressure). PAO is still better than straight Dino or "fake" synthetics like Castrol, et al. However, esters also have problems, seal swelling, and according to TSBs from both Ford and Honda, can accelerate organic clutch plate deterioration (what's inside the 4EAT?).
IMHO, it's all in the balance of the formulation - heavily weighted by the additive package - no pure oil, PAO, or ester (or combination of these alone) is any good.
We need a chemist/tribologist on the forum - and we need analysis to tell us truth - else we just trade opinions & hearsay (like I've just given) around 'til we all get tired.
but then again...trading opinions...at least it's usually fun
