On the topic of speakers, one thing that rarely comes up is the physics of the output section of the amp and the cabinet desgin, and their impacts on what we hear when swapping speakers and going for tone.
For example, if we have two V30's in a cabinet of any sort, the output section of the amplifier will "see" a certain type of load. But when we swap one of of those speakers out for something different (same ohm rating but different power handling), the power section is going to "see something different. Same goes for the impact of cabinets (ignoring open baked cabs on this thought). So two identical speakers will impart the same pressure inside the cab. But what happens to the "weaker" of the speakers when the phase draws the cone inward? Can the "weaker" speaker travel as far inward due to the pressure of the "stronger" speaker pushing it back out? Is the power applied to that speaker fully utilized? How does it impact the output section of the amp?
And things like this actually keep me up at night.....and I have to tell myself to shutup and just play my rig in the morning!