My 2000 Honda Prelude (Base Auto) indicates it requires "Premium" 91 gas. Can I use Regular 87 and be fine?

I would think that if the manufacture states to use Premium gasoline it is because the engine is designed to run at that minimum grade (but some people seem to think it is a scam). The previous original owner used Regular 87 octane and the Prelude seemed to run like it does on Premium 91.(?) However, I am unsure if there are serious long-term consequences that might transpire down the line and that is my main concern. For now I will use Premium 91, or at least Plus 89, until I can receive an expert's opinion. With that said, would Plus 89 satisfy the octane "Premium" requirement when in areas that do not have access to higher octanes or is Plus 89 not really any better than Regular 87?