I was riding 48/16 and switched to 48/17 a few months ago. It felt noticeably easier at first, but I grew accustomed to it, and now I actually prefer the new ratio. My reason for switching though, was solely for tire life in skid patches- I was totally happy with the feel of 48/16, and was hesitant to go lower. Based on my own experience with how much easier the 17 felt at first, I think the 18 may be too much of a leap, but it's really only for you to say. If skidding is at all a factor, the 17T will offer 17 patches, while the 18T will offer 3. For what it's worth I run EAI Deluxe cogs, ordered from Retrogression, and like them a lot.