91 is all that is readily available in my area, but I can get 93. I can even get 100 race fuel but I think that would be useless without a tune to use it properly.
I will say that I have noticed a performance difference between 91 and 93, in sport mode. Like the RS I had before this, and my GT350 now, the performance characteristics change considerably.
I have my GT350 tuned by Lund, and when running E85, the car picks up some considerable power. I'll look to do this with the MKZ a little later down the road, after my little PTU scare, I want to be sure the car is well-sorted before I go messing with warranty coverage. It sees close to 60 miles per day and other than that one incident, it's been rock solid so I'm not TOO concerned.
As for MPG, I see about 17-21, average use.
FWIW - I had a 3.0 FWD as a loaner and I would ABSOLUTELY spring for the AWD with this car. The power felt similar in take off but you can easily tell where the power overdrives the front wheels in it.