Go with any of the major brands. Personally, I use Castrol GTX on my '95 325i, and with engines this old I don't see any advantage in using synthetic oil, although some may disagree. I think similarly about the "high mileage" versions, figuring that regular oil and filter changes, based on type of driving, will do the job in removing any sludge and other contaminants. Don't use any additives, whatever you need in that regard is already included in the modern formulations.