Why meth? Its disadvantages outweigh its advantages when mixing with fuel imo. Unless your just running solely on meth, its a bit of a pain in the ass. As already stated you need to run more of it to make the same bang. It absorbs water extremly quickly turning it into a goo like substance so you must flush your fuel system out after use not just your engine for corrosion purposes but also to clear your injectors and mainly the fuel filter which i guarentee will clog in no time. Many cars that run meth run a specific filter or no filter at all. Water absorbstion can also lower octane which means you could get detonation and loose an engine.
E85 is a great option but your map will require 40% more fuel to make the same bang. This opften requires bigger injectors, bigger fuel pump and ecu management which all = $. However the rewards are there for the taking. A starlet member here recently did back to back tests with c16 vrs e85 pump fuel. Both made identical power (approx 290whp) but the e85 gave another 65hp of midrange power due to more ign advace being able to be added. E85 also absorbs water if left but at a lower rate. People here reccommend a fresh tank every 2 weeks at least, which isnt difficult becuase your using 40% more fuel.
This guy has the right idea. It is just industrial paint thinner. If your just after an octane boost then this is what your chasing. 10% will give a great safety buffer or you can add timing. Or you can go 20% and wind even more timing into it, all without changing your fuel map. I run a bit when racing as a safety buffer. Tune for pump fuel then it gives you piece of mind if things like intake temp ect changes. Its also dirt cheap and readily available from any paint supplier in bulk.
The down side however is that its not kind to rubber. Contact causes rubber to harden and eventually crack. This means your fuel pump, lines and even injectors and regulator. Meth will do this also. All the people I know running it havnt had any troubles yet though.
If your trying to chose a better fuel for race/street then e85 is the way to go as long as you have supporting mods. If your just after an octane boost then you can run tolulene or just continue buyin octane booster
Cheers
Harry