I used to go to SanFran monthly and had a good deal with Hertz where I always got a V8 Mustang for the price of a mid-range.
I got an invite to the Sears Point race-way as part of a BMW owners club and took the rental along. They offered me a run. I had some fun but also ran low on petrol. I went to the pumps they had on site and noticed a 107 octane pump. So I filled it up as you would given the opportunity.
I can confirm that it went faster. Lots. I also got evidence, no rear rubber left when I handed it back to the Hertz desk at SFO ! I got a dirty look next time I went to rent and they only gave me a V6.
