Along the same line of thought, are venturi filters or venturi size changes going to do the same thing as nitro changes?

Popping in a head shim isn't that tough a job, nor is adding an air filter or another layer of panty hose discs. Not only is carrying around two or three jugs of fuel a PITA, just getting a decent fuel in more than one percentage of nitro content is about impossible around these parts in the last year. The LHS dropped Powermaster and gets us CL peons SIG fuel...in quarts...for about $10/each. Not going there!    Steve

I think there are at least two things going on. 

First Nitro brings some oxygen to the combustion process, so it allows you to richen up the mixture (more fuel) and still burn it efficiently. So that is like having a larger venturi that lets the engine breathe more air (with oxygen) and bring in more fuel. In both cases you are burning more fuel, so that gives more power.

Head gaskets help change where the ignition point occurs. That can help or hurt power "depending" . With 1/2a at least, when I go up in Nitro (serious increases up to 25-30%), I also add head gaskets so preignition doesn't occur.

I am sure changing gaskets will affect power, but I am not sure how easy it is to pre-figure it out. I am sure some guys have.

I think the easiest may be the air filter trick- which is equivalent to changing venturi size (small changes I think). If you tune up the engine so that cool dry days use the most filter, then when you hit the hotter/more humid days you strip off the filters.