Excellent post!

One addendum to ethanol. Even though it has less energy density than gasoline, in a properly tuned engine ethanol will make the same power. This is because the ideal air:fuel ratio is different for ethanol, so you can get much more fuel into a cylinder. The accepted gasoline air:fuel ratio is 14.7:1, while ethanol is 9:1. Doing all the math in a perfect scenario ethanol will make 99.6% of the power gasoline will in the same cylinder. MPG will suck, but power is about the same.

Again, this assumes the engine is tuned for ethanol, or has special sensors that allow to vary it's fuel map based on the ethanol ratio detected. Our disco's don't have those features.

 

Excellent post by L33Disco2 on octane and how engines work. If running high loads/hot temperatures, I would always opt for a slightly higher octane as those situations create stress that can induce knock.

FWIW, my "seat of the pants" review of 90 vs 93 says that the 93 performs a bit better. I notice better pull on uphill sections although I never had any codes or anything with the 90 pure gas.

 

You should notice more power with higher octane in an engine that can dynamically adjust timing. By raising the flash point of the fuel you can move the spark timing further into the engine's rotation without risking preignition that would occur due to heat and pressure. Think of riding a bike up and over a ramp, the pedals are really hard to press as you get to the crest but then as you transition to the down side they get increasingly easier. This isn't actually what happens in an engine but should give you a mental picture of the spark happening a few degrees before or after the peak of the incline. Before the peak is preignition which counters the rotation forces and is really bad, too far after the peak and you get into valve actuation which is also bad but for a different reason. Those few degrees in between make a big difference in performance.