Cam advice wanted

You can not mill that much off the head to require 91 octane. The heads must be disassembled for milling. I would not go this route myself since there is a lack of money (Your complaint about an extra $10'per week/tank) and the gain small.

Once you mill the deck, the intake face of the head must also be milled to keep things aligned and correct. To mill the head as much as you would need to get a meaningful ratio, you'll run out of material on the intake face of the head and you will need to mill the intake itself. This becomes a pain in the backside.