I would imagine the Trek 7.5 FX to be a kilo or two heavy than a "full on road bike", yet it will afford you the luxuries of mudguard clearance and easy rack mountings. The extra weight means your acceleration will be a little slower and hills will be slightly harder relative to a full on road bike.
What the full on road bike will do, is give more choice on positioning your hands and body. If you are stuck in a crosswind, you can get your hands down onto the bottom of the drop bars for a full aero tuck. The drop bars are better for bracing onto if you accelerate fast away from traffic lights. And, they are also good for giving a variety of different positions for holding the handle bars which makes for more comfort over longer distances.
To my mind, a "full on road bike" really means a racing bike, and that possibly means it won't have concessions to fit mudguards and a rack easily. That said, it will feel much nimbler, a bit sportier and that little difference can mean a much more exciting commute. The geometry of a full on road bike is usually quite aggressive to maintain frame stiffness, fast cornering and give a more aero position.
It might be possible to get a not so full on road bike with slightly relaxed geometry for a bit more stability and comfort, clearances for mudguards and braze ons for fitting a rack. These take a little more finding out though and actually either tend to be low end frames which are nearly as heavy as hybrid counterparts or much more expensive frames that are really, too good for commuting!
You might be sensible looking at a touring bike, which again is a road bike, but it will accept slightly wider tyres, have all the clearances and brazes on desirable for commuting and a wider range of gears.
People mention cyclocross bikes. These quite often come with adequate clearance to fit mudguards and rack braze ons, but if you want a womens specific design you will be hard pushed to find one. They are also probably getting on for as heavy as hybrids and tourers.
Lots of different manufacturers develop bikes with different philosophies. There is quite a lot of crossover between them. It's worthwhile taking time to go to a big bike shop and have a look through their range. And also try a few. Work out whether you are more comfortable on a normal frame, or a womens specific frame. If you are looking for a smaller bike, than you may find it harder to get what you want, although it's more than worth perservering. It's your bike. It's a very personal choice.
I'm a big believer in having different bikes for different purposes.
And, I cycle because I enjoy it - if I go faster, it'll take less time, so less time enjoying myself...
