The MP3 required higher octane more for the ignition timing. And the Mazdaspeed required higher octane to handle the boost. Since you don't have the MP3 ECU, you probably don't have the more aggressive timing curves. Other than the cams, none of the mods you listed will affect your octane requirements. Cam timing can affect your dynamic compression ratio. However, I don't think the cams would change your dynamic compression ratio enough to justify premium fuel. Do you have the FS-DE cams (j-spec cams purchased from Mazdaspeed) or cams from an MP3 or MSP? If the latter, than they're the same specs as the P5. Consequently, there will be no difference in your dynamic compression ratio.
Regular will do. Looks like I'm voting with the census.