Doesn't matter how new the oil is,there will always be friction inside an engine,small friction but it is there.If the engine is old,it's probably pretty worn(cams,bearings,rings),so why wouldn't you exceed the '90s requirements with something that could provide even less wearing?Even though I know it's over the requirements,I prefer to use only expensive oil to prevent any future engine rebuilds which will be expensive,much more expensive than the price difference I pay for the high quality oil.Anyway,the difference is like 10-15euros/gbp/dollars per oil change.If you buy a set of piston rings and a set of bearings it will be like 2-300,that's 20-30 oil changes.Really,the price difference is worth it.I use only Ester base oils,but I don't want to start a new discussion about this,I just think it is way over anything fully synthetic on the market.