Follow the owner's manual. Use premium unleaded.

Even if premium unleaded is 20˘/gal more expensive than midgrade, you're only spending about $2.50 more per tankful.

Detonation is what kills motors. By using gas that doesn't meet the OEM octane requirements, you risk detonation and significant engine damage.

True, the ECU has a knock sensor and it will disallow the VTEC switchover should it detect detonation. But for such minimal savings, it's a moot point IMO.

Like I said before, follow the owner's manual.