A synthetic 10W-30 is an reduntant grade. It's cheap to make and has proven to be no more shear staple than a premium syn 5W-30. And with a VI in the 140 range a total waste of money. Either stick to 10W-30 dino or treat your engine to the full benefits of a high VI 5W-30 syn or 0W-30.
CATERHAM Yes, thank you i was thinking that!
Is today's Dino SN oils in 5W-30 perfectly fine too?
Im trying very hard to break out of the "old thinking" that a 10W-30 is in fact more stable than a 5W-30, in this case two SN "dino" oils (lets say Supertech, side by side, SN 5W-30 and 10W-30) and am thinking 5W-30 for the Contour twin i have. Thought of 0W-30 too but the engine is a big unknown so it seems a waste.