I was a messenger in Boston and NYC. Had a Frejus track bike in MA with a front brake actuated by a bar end shift lever with ratchet removed. 88inch gear caused tendonitis in both knees in short order: Starting out in that big of a gear 100 times a day was what did it--young and dumb..
In NY I had a road bike which was superior in many ways--I could take long runs to Brooklyn or Queens and go much faster than a fixed in less congested situations, especially going down Second Ave where it was easy to hit 45mph.
Anyway, there were two brothers in NY who both rode fixed. It was hard to tell them apart, but you'd see them in passing, or be behind one of them and it was fascinating to watch: They did not go around obstacles, (pedestrians, cabs and buses pulling out, etc.), they rode
through the congestion and into whatever tiny opening was available. Always kept forward momentum. I'd be behind one of them and a car would pull out of a parking space "blocking" our path. They would take the same trajectory as that car instead of braking and waiting for a clear opening or shoot a gap 12 inches wide between a bus and a parked car. I'd be braking and waiting and would have to work harder to catch back up. Bottom line is to look for openings and stay moving. On a bike with brakes you'd be using them.
Also, slow cadence seemed to work for them the majority of the time. Guessing 60-65rpm was where they were at. Not saying that's right for recreational use, but that gearing meant a lot of the time the brothers were taking it pretty easy, but had enough gearing to go quite a bit faster when needed.