This is/was an interesting thread. I always thought the base 2.4 required premium - I have no idea how but I totally missed the past where it says it is designed to run on 87 octane with slightly degraded performance.
As for octone my understanding has always been the ECM is designed for a particular octone, and if you go over that you get no benefit, but if you go under it, you can get knocking and noticeable performance decreases. I had a 400hp '05 GTO and an older '98 Corvette, both required 91 octane, and if you went under that you'd get knocking. On the Corvette you'd get pretty bad knocking, very noticeable - and it would go away quickly once you got some 93 back into the tank and it mixed around. My gf at the time took the Vette out and put some cheap gas in it, and it ran like garbage, and that's when I figured out octone CAN (sometimes) make a difference.
I'll have to put some cheap stuff in my '07 Sky and see how it runs. The price difference between 87 and 93 used to only be about $.10-.15 back in the Vette days, so it wasn't a big deal - but now it's routinely a $.60 difference even though gas prices have only doubled.
Anyways - I was wondering about this, googled it, and this was the first result. Thanks for bringing it up and talking about it.