As with the OP, I also own a Trek 7.4FX, although I went down to a pair of 28mm Gatorskins and rode with clipless pedals. However, last year I bought a Giant Defy carbon endurance bike because I found that I still had a need for speed, or in my case, a need to ride less slow.
My anecdotal evidence is that I immediately picked up about 1+mph upon switching to the road bike. It's gotten better since then.
It might also be interesting to note that my crabon
machine is about 7-8 pounds lighter (approx 17lbs vs 25lbs) than the aluminum hybrid, so that should account for a little extra pep in your ride (as would a couple of extra gears on the cassette).
Either way, enjoy the ride!