Sheesh, finally a real answer. Thanks for the info on RON, that makes sense now.
But about the ECU, I read some posts (just from people on the forum, not like Mazda dsegners or head techs or anything) about the MP3 ECU vs. regular 2.0l ECU's (Pro5, ES). Someone said they found out that Premium is recomended because the MP3 advances the timing to aid in the extra 10 HP (I don't think that could give it all 10 HP, but I could be wrong). If regular 87 is used, the ECU can sense something (knock sensor?) and retard the timing to regular specs.
Now, assuming that this is true, how about this idea (just shooting in the breeze here):
Being a penny-pincher car (under $20G) it would make sense that Mazda would not want to totally re-do the ECU for just 1500 cars, so I'm wondering if they designed all ECU's for ther 2.0l to give the extra HP for premium fuel, and regular power for reg. gas? I mean, the MP3 is the only one recommending premium fuel, the only one with the extra HP, and without the better fuel, no extra power, right? So Mazda puts the same damn computer in all cars, tells MP3's to use premium, and there. Problem solved. Now the owners like me who put 92 in, well, they just happen to get the extra HP without even knowing it.
Aaahhhhhhh, one can dream, right?