Looking at sheldonbrown.com/gears, the difference in your cadence for various speeds would be:

Using 48-17 and 48-19 gearing on 700 x 23C and 170mm cranks,

8.8mph 7.9mph @40rpm
13.2mph 11.9mph @60rpm
17.7mph 15.8mph @80rpm
19.9mph 17.8mph @90rpm
22.1mph 19.8mph @100rpm
26.5mph 23.7mph @120rpm


The 19T cog will require 10rpm more to get the same speed as the 17T. My road bike has a cadence sensor and based on my riding experience, 10rpm is significant.