Can you post some examples of acoustic guitar? I'd like to see how clean they compare, transients etc. Can't really do that with a cranked up distorted guitar example.
If possible use two of the same mics and place them in front of the acoustic guitar next to each other. Send each preamp to its own track. That way you can record the same performance, using the same mics, through different preamps. It's really the only way to do the test properly. Same thing with some spoken vocals that would be nice also, just do it the same exact way.