I also don't understand the 5-pound target. Aside from dropping weight from the team, lightening up the wheels would probably give you the most bang for the buck. I don't know how much the disk brakes weigh, but I woulld ditch them for calipers or cantilevers.

It always amuses me how that people will spend big money to drop a few ounces from their bike and then add two (or four) full water bottles that must weigh a couple of pounds! Making sure that your bike fits properly will also make you more efficient and add speed.