Since the manual specifies 91 octane minimum, I use 91 if it is available. However, most stations around me only have 93, so it's usually 93. Sometimes a station has both but there is only like a 2 cents price difference, in that case I get 93. Usually 91 is like 10 cents cheaper though if they have both.

 

For the most part, SoCal only has 91. Zero issues with it ever.

 

I have used 89 octane in my GS for over five years. No problems. I get 25-27 MPG in town. I used 87 octane in my SC400 for almost 20 years without any problems.

 

I always use 87 in all my cars with a can of BG44K every 10,000 miles to keep the injectors clean. Has worked well for me for over 25 years of driving