I think a lot of fellows (including myself) have tried 87 octane before. In fact I think that 87 gets better mileage. I don't know the physics behind that but do a search and I'm sure lots of explainations will come up.

I've tried 87 and it runs fine. Just don't expect as good performance (or something).

 

I only run high test fuel..........I want performance over gas mileage.

 

The only performance decrease you see in using 87 octane is if the engine starts pinging.

Generally in winter, it's okay to use a lower octane rating because of the colder temperatures. In the summer, you want to prevent pinging with a higher octane fuel.

 

I have had my GT Standard for about a month now driving under 4k rpm with 80% city. I have filled it up twice with octane 92 chevron and I'm only getting about 300km per 50 L. The total mileage on the car is only around 800km.
Hopefully it'll improve later as the mileage increases, I'd be happy with 350.