Do you have to climb hills going to work or home? One big difference on the Trek 7.5FX is that it has only two chainrings, 50/34, and a cassette of 11-34. If you have big hills to climb like me, then that would be a bad choice especially if you are new to bicycling. You will find yourself walking yourself up some hills. Just like you, my commute is around 4 miles, but it involves climbing 300-350 ft over a distance of about 0.8 miles, or 90-105 meters over 1.25 km, and for myself, the gearing on the 7.5FX would be completely unsuitable. Even though I've been commuting by bicycle since Q1 this year, I still find myself using the 28-34 gear combination on my bicycle for the entirety of the climb.
By comparison, my current bike has 48/38/28 chainrings and 11-34 cassette so the gearing goes much lower for the times when I have to climb those hills. Although, I seldom find myself in my big chainring. I wouldn't miss it if it were not there.