yeah i think the worse the base fuel the better the gains you'll get once mapped for using a methanol spray. When doing these on 3sgte engine in the 350-400bhp mark depending on how much you inject typical 10bhp gains, if you then raise the ignition advance up and boost to match i was safely seeing 25bhp on a 400bhp car. Power delivery felt smooth as well. But i would only ever advise this on a good quality system that can detect low methanol, blocked jets etc. anything that it can throw the car into a safemode if for any reason the methanol isn't spraying. as if you do get a blocked jet or run out of methanol its bye bye engine as it'll be mapped for that extra det protection. I don't think the AEM is that advanced to do that. the best onces i've found are the aquamist 2D kit upwards or the new line or kits there doing.
If your not mapping for it don't expect a huge amounts of gains, if anything it normally takes power away as the methanol acts like additional fuel and overfuels, causing you to loose torque in the midrange, and sometimes causes a small misfire as the methanol is first injected, The better kits like i mentioned above will bring it in gradually and match what it injects to the fuel injectors to give a fuel/methanol ratio which you then tune with the jets, so you run a 1:20 setup regardless what the fueling is doing you will maintain that ratio.
Tim