Surprised at Gasahol Result

My son and I had a surprising experience with some 'up to 10%' gasahol today. We have been running his new 340 around in the last few weeks, and using nothing but non-alcohol 93 octane fuel from a local no-name chain. Their pumps were out today, so we put in 5 gallons of Shell 93 octane gasahol with up to 10% alcohol. We drive 1.5 blocks and stopped for a red light, and looked at each other and said "Is this thing idling smoother?" We drove on home 5 miles up a 1000' foot climb, from 55-60 mph straights to a 30-40 mph twisty section, and commented at each phase how smoother the motor felt and sounded. Pulling into the driveway, I hopped out while it was idling in gear to listen to the exhaust note, and darned if it did not sound more even. (We have been tweaking on this thing for a few weeks so are really tuned into the sounds....)

FYI this 340 has 10:1 SCR, AL Edelbrock heads and intake, Crane Z-268 cam, and Spitfire headers. All I and figure is that the fuel volatility is better and making it fill and run more evenly, or the alcohol is effecting the combustion process. I expect this engine to be somewhat sensitive to fuel but this is something I have never seen. (The only more dramatic change I've experienced in my time was a load of really bad gas!)

If anyone has any other ideas why, I'd like to hear them and learn. I read this thread to glean the comments there:
http://www.forabodiesonly.com/mopar/showthread.php?t=327846&highlight=alcohol