A general reply to lots of posts in this thread:
Ethanol in marine 2-stroke engines here in the PNW has caused all kinds of problems. Also if you get any water in ethanol gas, it will mix wit the ethanol and phase separate, whereas in E0 gas the water just goes to the bottom. Ethanol will also extract a lot more water from the air around it, whereas gas will not. Ethanol is also harder on rubber parts and aluminum engines. Give it time, or use it in an engine not designed for it and it will be worse. I avoid E10 in my 2-strokes if I can, but by all means, use it if you like it. 10% ethanol in gas is the maximum that any saw company will warranty though.
As for Mastermind running regular gas (if that is indeed the case) I believe that is a huge mistake, especially given the fact that he increases the compression on his saws with his cut squish mods and he commonly advances the ignition timing. The reason they came up with supreme gas was to avoid detonation/pre-ignition/ping/knock/flaring in higher compression gasoline engines, as well as running engines at high altitudes (which is why AvGas is still used in airplanes). Increasing the compression in a saw will (not might, it simply will) increase the likelihood of detonation. Detonation will cause pitting damage around the squish band of the piston and cylinder, and uneven flaring can and will cause uneven down-pressure on pistons and cause them to tilt slightly. That can cause piston skirt and cylinder scuffing, or a ring catching a port. Maybe a dyno does not care about detonation, but your saw and your wallet eventually will. If you wanna run regular in your ported and modified saws, go ahead. Not in my stock or modified saws though, thanks.
Most all 'good' chainsaws are designed to run mid-grade 89 octane gas (not talking Chicom here). Octane starts to drop as soon as it leaves the refinery. By it has reached the gas station mid grade gas is likely down to 87, and by the time you put it into a gas can and store it for a while, it will be down to 85 or even less. Add premix oil at 50:1 and the octane drops another 2 points, or 3-4 points if you run oil at 32:1 So now you are down to 83 octane or less. Give it time and the octane will sink farther into the 70s to the point where it becomes bad gas. That is where the gas starts to flare and detonate badly and does damage to the engine. For that reason I add stabilizer to my gas. Stabilizers like StaBil and SeaFoam will keep octane as high as when you added it to the gas for up to 2 years. It cannot boost old gas octane though. Stabilizers will also help keep the ethanol in E10 gas from phase separating, but only to a point. So I add StaBil red formula to my E0 premium gas right at the station when I fill the gas jugs. My ex insists that regular untreated gas is fine for her saws, because the county work crews use it in their saws. I prefer not to sink to the level of the government myself.
Now there is the case of the opposite here, using LL100 or AvGas. There are several issues with this gas, one being the lead in there. The oil companies originally dumped lead into gas as a cheap way to raise octane, and they made a lot of money off if it. They knew it was highly toxic, and there were many deaths at refineries over the years as a result. Large companies are greedy though, and have no regard for human life. Just look at GM's decision to not replace a 59 cent spring in their ignition systems. At any rate, TEL is highly toxic. Lead smells good and tastes sweet, which is a bane to humans, because it causes havoc with your nervous system. Breathing lead fumes will affect your brain and lower your IQ, lower your motor function, and diminish your senses. The reason they banned lead in auto gas was the fact that the LA CHP officers had an average of half the lethal levels of lead in their bloodstream. The average American had 2-10% of the lethal lead levels in their bloodstream. Since banning it, the bloodstream lead levels have all gone way down, and the relative heath of the average American has gone up as a result. You would be well advised not to run leaded gas where you breathe the fumes. The other thing about lead in the gas is that it can foul your low end bearings, as well as your spark plugs. While lead was used as a lubricant in the valve train in pushrod engines, saws are designed to run lead free gas where the added lubricant qualities of lead are not desirable. The other issue with Avgas is the high octane. If you run a saw at high altitude this may well be an advantage, as altitude is another cause of pre-ignition. However, using a premium grade unleaded auto gas would likely be as effective in preventing pre-ignition at altitudes up to 10k feet. If you do use Avgas, please do not run it on my property or near me.
...You might be right. It could happen. The only airport that ever told me no about buying av-gas was Sacramento International and that was probably because they have the usual big-city airport security thing going on. 
