If you try this, don't forget to reset the ECU's air fuel map. Basically start the idle relearn, or you will notice a lot of predetonation until it eventually figures out the new optimal mix of air and regular fuel.
It didn't work out for me when I tried mid grade a few years ago. Probably needed a map reset, but I had really bad knock when slowly accelerating somewhere between 1500-2000 rpms.