1) he still hasn't answered what the compression ratio is, that will tell you if it's required

2) being that it's upper model of the prelude and says use premium only then why argue with what the manufacturer says? Honda has nothing to do with oil/gas prices, they certainly don't benefit from it, so why do you think they would they say use a more expensive fuel? If anything it hurts them because premium only cars will discourage people from purchasing them.

3) Worse comes to worse go down a grade until it starts to knocks then go back up a grade, it's not going to hurt it it.