compression difference

As said above 10.5 on the street maybe 10.8 with aluminum heads anything more and you will have to run fuel. You are right that you are in no mans land where you are but 13.1 is race only and the motor will need lots of attention, where you are at now you can mix some 100 octain sunoco with your 93 50/50 and you should be ok. Still going to be expensive to operate.

I would give up the power and lower the compression to make it a pump gas motor you will be much happier in the end.