I have put about 7000+ miles on a Nexus8 hub / Surly Crosscheck bike, mostly for commuting in an area with some moderately hilly terrain. This bike has upright Nitto Albatross bars, so it is set up for more comfort than speed, but I average about 13.5 to 14 mph on my commute rides (typically 20-25 miles round trip). I use a 42 chainring with a 21 cog on the hub. Thie gives me a low enough gear to climb some fairly steep hills at 5 to 6 mph, and also provides a top end that will let me keep pedaling downhill at speeds up to 26-27 mph. Beyond that speed on a long downhill, I tuck down and coast. The gear spacing seem fine to me whenever I ride the bike, but I am not too picky about cadence.