[RockDoc]

I'm not as up on it all as some of the 80s guys (look there for a ton of info and debate) but I think the add-pack is more important than whether the base-stock is syn or conventional. I used to run Mobil 1 10w30 year round, now I run Rotella T conventional 15w40 summer and Rot T syn 0w40 winter. Lots cheaper, and I suspect much better in terms of additives.