The zinc is only used when there is actual metal to metal contact in the engine. Hopefully the oil will do its job and this will rarely occur, but if it does, the zinc compounds react with the metal to prevent scuffing and wear. Those of you with high revving, air cooled motorcycles or turbo charged cars or bikes might want to look at the oils with the higher zinc content. More doesn't give you better protection, it gives you longer protection if the rate of metal to metal contact is abnormally high. High zinc content can lead to deposit formation and plug fouling.
Synthetic oils are superior lubricants compared to traditional petroleum oils.
You will have to decide if their high cost is justified in your application. You've got nothing to loose. We're taking all of the risk. I can concentrate on driving the race car.