I think another member on here (BGTV8?) originally posted this, but FWIW, here are some independent lab test results on changes in octane from various additives. I'll see if I can find something more authoritative, but for now, this is seemingly impartial and informative.
Note that they are going by RON, not AKI (RON+MON/2). TO get an approximate, multiply the RON by .95 (e.g., 96 RON is approximately 91 AKI).
http://www.fueltechexperts.com/2008/...which-is-best/