I range from 16-18, depending on the day. 18 only for polo nights or spinning work. 16-17 daily use depending on my mood/weather and the 16 sees some sprinting days and long rides but mostly on 17 as you guessed. I have the 18/17 on one wheel and 16 on the other wheel. more important than just my cog is that I'm running usually a 47chainring but have gone as much as 49 and as low as 42 on the street. I guess I've switched around quite a bit