I have used 89 mostly but filled up on 93 today to get a free car wash. I started a new topic, but really copied what Puma Speed does in the UK. I think the drop in filter helps, but this mod also helps get air straight in from the side reducing that pressure wave previous discussed.
White Platinum Tricoat Metallic
2012 Ford Focus Titanium
Handling Package Nitto Motivo's
Borla Exhaust with UltraQuiet resonator
K&N X-4870. Steeda RSB