Any of those FX have better gearing than your bike, i would recommend the 7.2 this one have better components than the 7.1,better value for your money as well,you can air up the bike u have now and try slick of u just want more speed,you have a comfort bike with suspensions and upright riding position,the FX is more of a fitness bike,u have to learn to ride in a new position with the FX set up.
Here is the comparison of the 3.
http://www.trekbikes.com/us/en/bikes/compare