I've generally used Motul 7100 full synthetic 10W40 (one step down from the 300v) but have been giving BellRay EXS a go for the last 2 changes. Engine is quieter, starts easier and gear changes are smoother. Google it; you'll be impressed with the blurb, and it seems to work. Costs around the same as the Motul 300v. Nothing wrong with Shell, Castrol, Silkolene equivalents for that matter. Semi synthetic would be fine for a relatively stock engine. Main thing is that it is suitable for a wet clutch and preferably a known brand.