light commuter
Salsa Casseroll or Soma Smoothie or ES would be good options. Drop the backpack and get something like a Carradice Barley seatbag. It gets the weight off your back and centers it on your bike. You could easily build a reasonable light-weight Casseroll or Smoothie that would weigh 20-22 lbs. BTW, with a Carradice bag you could continue riding your current bike, although fenders would still be an issue. Here are photos of several of my road bikes set up for commuting with my Carradice bag. The Merckx Corsa and De Bernardi are racing frames, and the Bob Jackson is a touring frame. All of them weighed about 21-22 lbs. built up with DA/Ultegra parts, Open Pro wheels (not including the seatbag and lights).