Given the miles you are putting in, you are more
than ready (as if there is some magic rite of passage).
The road bike should be lighter, and be easier all around
to ride. I think you'll see a large difference in handling.
The roadie should have a more aggresive geometry.

The one caution I would suggest, don't get too caught
up in the boy racer aspect of it. You might do better with
a stem that is a bit higher than what most race type bikes
show (A quill stem here is a good thing), it would be a good
transition from the flat bar.
Go to LBS and test ride as many roadies as you can
(A.Troll does this best), and get a feel for the bikes, then
you should know the answer better than anyone else here.

Marty