I have two 4900s that I ride to work (though, to be fair, my commute is only three miles or so). I have one set up with 1.5" tires with reflective sidewalls, full fenders, and an Air Zound horn (loveit!), and another with just 1.25" slicks for sunny days. I also mounted a SuperFlash to both bikes' seatposts. I use a couple Knog frog lights and 3-LED sigma clip-on front light.
I didn't bother swapping out the fork on either - I don't mind the cushioning when navigating Boston/Cambridge's potholes and constant construction.
Also, I'm jealous your 4900 has disc brakes - sure would come in handy November-March....