I've been using a 1x9 speed drivetrain on my early 90's Specialized Crossroads for about a year and a half now, and have been really pleased with my gear range and the simplicity of it. Since moving to Hawaii it's been my only bike, so it serves a variety of roles- commuter, errand bike, road bike, and trail bike. I've implemented a quick-swap cockpit system with three different setups- a drop bar Richey Beacon, a Map Ahearne bar, and a Jones loop H-bar, so it sorta feels like I have three different bikes.
Since I use it on the nearby singletrack trail system, I need a decently low gear. I've been very happy with the Sunrace 11-40 cassette paired with a 34t front chainring. With my 40mm wide tires, I've got a gear range from 85" - 23". If I'm using my 45mm knobby Tufo Swampero trail tires, the range is 87" - 24". I use a MicroShift 9-speed downtube shifter paired with a Shimano LX rapid rise, non-clutch, rear derailleur (RD-M580) and a KMC 9-speed chain. Even though the derailleur is only rated to a 34t largest cog, I have no problem at all on the 40t cog. I wonder if it might be due to the rapid-rise function where the spring is the most relaxed in the largest cog, that it's able to handle a +6 tooth increase from the max rating.
I've toyed with the idea of maybe adding a small chainring and manually dropping into it when I ride off-road, and that would allow me to have a tighter cluster in the cassette. But like I said, I'm super enjoying this 1x9 system and since I can do all the riding I need with the current setup, I will probably keep it that way for the foreseeable future. Mahalo,
~Mark
Kailua, HI