Joe,
If most of the LGT failures are due to the screens becoming clogged, then it's not a viscosity issue correct?
Or are you thinking that they're being clogged because the oil is failing due to the viscosity index improvers in the oil failing and turning to sludge? Maybe a deposit problem too?
I did a quick search on Opie and noticed he was using Motul a few years ago.
FWIW, I believe Terry Dyson recommends mainly 10W-30's to most of his customers. That's only based on what I've seen from his customers posting their uoa's here. I saw one modified STI owner running RLI HD 5W-40. Other Subaru turbo owners are running RLI 10W-30, Rotella 10W-30 (every 3,750 while under warranty) and some other 10W-30's, IIRC.
-Dennis