Most octane boosters only raise the octane by points and not numbers. I.E. pour in a bottle of STP to a tank of 92 and you may only get to 92.3.
I read a study about different octane boosters and their abilities to raise the RON and it gave a pretty good list of what worked and what didn't and to what degree each did. I'll try to find it for you. But basically most was not impressive nor effective enough to raise your petrol by actual RON numbers... not points
I looked at toluene, xylene, etc really hard but it is not cost effective anymore. Especially what they charge in small quantities to the average consumer. If it were to cost you 50 dollars in petrol and then you added 2 or 3 gallons of toluene, you may end up paying 70 or 80 dollars per tank.
Plus if you live in a state, such as mine, that is a heavy methamphetamine making dump, big brother would be watching you. Also, a lot of distributors will not sell to you unless you have a bonafied business that would need those chemicals. Plus the cost and having to keep 55 gallon drums kinda would stink.
I tried Torco Accelerator for about a year and it was some good stuff but again, cost can be prohibitive and the logistics of having it/ordering it kinda sucked. Basically I used 16oz per tank and typically bought it in 32 oz six packs or 6 quarts per case for about $120 per case. This resulted in 10 dollars per tank, extra. A 5 gallon drum was about 220 shipped and resulted in a yield of 20 quarts. Cost was about 11 dollars per quart and roughly 5.50 per tank. At said ratio of 16oz per tank.
At those ratios I was probably raising a tank of 91 to about 93.
A 5 gallon drum would have lasted me about 20 months.
I got tired of the ordering and mixing and just tuned for corn. lol
Meth/water/alky might your best option. Get a good kit with fail safes. I have even seen guys use window washer fluid. The good winter kind has something like 30 ish percent methanol.