I'm not sure of this, but it looks like Trek may have streamlined its FX line for 2017 and changed the naming scheme. As such, I'd bet the 2017 FX 3 is the equivalent of the 2016 FX 7.4. The only real difference I see is the rear derailleur went from Deore to Alivio. That's down one step in the Shimano hierarchy, but since it's one year newer it might actually be the same technology. As for pricing, I know that Giant dropped their prices by a good bit for the 2017 models compared to the 2016 ones, so maybe Trek is doing the same thing.
Of the bikes and prices you asked about, the FX 3 makes the most sense. I have a Fuji which is pretty much identical to that one, and it has served me well for two seasons so far. My typical rides are about 15 miles on country roads, 3 or 4 times a week, with an occasional 30+ miler thrown in, as well as leisurely rides on rail trails. It's a great bike for that purpose, so I'm confident in saying the FX 3 would be as well.
If you've got a Giant dealer nearby, you might also consider the
Escape 1 which lists for $600.