Brucemetras, I am right there with you buddy. I have recorded times with my Dahon Helios converted to singlespeed at 62 & 66 gear inches, with and without a Zipper fairing. They both come in around 51 mins 30 seconds to 52 mins 15 seconds - a 45 second spread regardless of traffic, wind, etc. I was surprised that my 62 GI was not substantively slower than at 66.

One day, it may have been I simply caught more green lights or whatever, but I remember spinning harder and my recovery times at the top of hills was quicker, but I set a time of 47 mins 12 secs with the 62 gear inches. This surprised me being a "slower" gear. I guess based on terrain, rider strength and cardio capacity, 62 gear inches is the sweet spot for my commute.

Its nice having the option of lighter gears especially if one is feeling tired. If my commute was flat, I would probably ride between 72 and 78 gear inches and spin it. But I need low enough inches to make my highest hill. The single speed IS more zen. I also hate the feeling of the derailleur slapping forward when I suddenly decelerate. And having gears and making shifts definitely involves more brain cycles than running a singlespeed.