Here is some very good information regarding octane boosters. 104+ raised the octane a tenth of a point. NOS octane booster fared better but it used an additive called MMT which is not sutable for long term use as it leaves metalic deposits in the combustion chambers and piston tops.
There is also some info in regards to blending your own on page 2. I know it's a 'vette site but the information is from one of Rockett Brand Fuel's chemical engineers.
http://www.idavette.net/hib/fuel/index.htm