I like the FX3 over the VFR5 for a couple reasons, the FX3 is lighter, has a carbon fork which is lighter and much more forgiving over bumps, it also come with better derailleurs. Weight is really a big thing to be looking at with the type of riding you will be doing, and a couple pounds makes a big difference.

A lot of Trek dealers will "rent" you the bike you are interested in, and you can ride it for a couple days. If you buy it they normally refund the rental cost.