By skyforbes 
The journey took us 25 minutes (thanks to a wonderful friend for timing the route out) and at no point did we ever catch up with the walkers. The bus driver was incredibly wonderful and accomodating plus the general vibe inside the bus was pretty chill. The bus was pretty packed (we didn't exactly help there lol) but not many issues arose during the bus trip.
I noticed that we sped up as we went towards 5th/6th Avenues and that we were pretty fast from that point onwards. It seems to me that from 1st to 5th things feel like a bottleneck. Unfortunately this was my first time riding the M34a SBS so I can't say for certain if this is true…
…but if a group of people can outwalk a Select Bus Service bus for (almost) it's entire route that probably should tell you something.