Use this calculator:
http://home.earthlink.net/~mike.sherman/shift.html

Insert 16, 17, 18 or whatever and 44, 46 and 48 in the chainrings and your're set. You'll get gear inches all together so you can compare them. If you go down to the "Speed Over RPM Range" you get a nice visual idea of the relationships of the different ring/cog combos---check the sort box and it will lay them over each other for you.