This is not a literal question so I'm not looking at / for specific models, but more a theoretical one. Let's assume I could choose between two bikes for commuting, one with a modern 22 speed drivetrain setup and another with a single speed. The geared bike weighs 30 lbs, and the single speed bike weighs 20 lbs. They cost around the same (not that it makes any difference in this particular scenario). My commute would be about 8 miles each way, so 16 miles round trip, in a major U.S. city with normal traffic and not too much elevation gain (say around 150-200 ft or so, also round trip). Let's assume the city has 4 seasons and I would commute every day. Let's say I weigh around 140 lbs. I've tried to outline both the pro's and con's below, but I'd like to figure out if I'm missing something.
- Gears may allow for a faster overall speed if there are long uphill or downhill sections, or long open flat stretches with no traffic
Single Speed Bike
There is a weight reduction vs the geared bike (in this scenario about 6%) which may result in an increase in acceleration, especially when accelerating from frequent stops in traffic or going uphill
There is a slight increase in drivetrain efficiency due to a lack of derailleurs and a "perfect" chainline
If the rider regularly encounters traffic or does not ride over any substantial hills, I believe the single speed may actually be the better choice in most urban commuting scenarios. Given all of the following information, which one do you think would be faster and why? Any real world experiences and results would be welcome as well. Please disregard any other benefits not related to speed, such as the single speed having less parts = less maintenance and more reliability, generally more quality for the same amount of money spent on a single speed, etc.
Edit: I feel like everyone is missing the point of this question, so I thought I'd clarify. I own a modern 22 speed bike, a fixed gear, a single speed, a single speed mountain bike, and a relatively light 3 speed IGH. As I mentioned before, I do not want to hear about the pro's and con's of actually using each one for commuting in terms of cost, maintenance, etc.: I know about these already having owned them. I just want to know, given my particular scenario, which one you think would be faster and the technical reasons why you came to that decision. I'm not interested in discussing anything other than implications on commuting speed for this particular question.