This was a while back, but when I ran my 12:1 440 on the street, I used the NOS brand octane booster on occasion. They had a couple different versions...the one I used was the "race" version. It seemed to be way more effective than any of the other off the shelf brands at the parts store.
I normally ran either 100LL AvGas or a 50/50 mix of 93 and 110. When in a bind, I'd run 93 w/ that NOS race booster.
Not even sure if they sell it anymore as I haven't had a need for it in 15 years, lol.

I know this really doesn't help you. Just thought if they still made that additive, it might be worth you trying it.