I loved my 16t, and went to the 18t because most of my rides are longer ones. I think I'm in 5th occassionally now, when I'm still in 4th! Don't search for 6th as much anymore, but have. Lost some top-end speed, and gas mileage sucks when running wide open in 5th with the 18t. Mostly from the lack of torque. Overall, I'd recommend it. The 17t probably is the perfect compromise, but maybe not worth the trouble (which it isn't) to change. I still may put my 16t back on one day to compare - I never had a complaint one with it on - even after 400+ mile days. I do like the 18t around town - 2nd and 3rd gears running speeds from 20-50 mph - riding the higher revs. That aspect I had never appreciated with the 16t, but maybe more from lack of opportunity. I had 6-7k miles on my SM before I changed the sprockets, and have put probably 2500 miles on since. It's like learning to ride a new bike all over again.
Change is good, whatever you do. Not much can't be undone.
