Are you going to the same destination over and over, or to all sorts of destinations? Because if it's the former (say Mon-Thu every week at a big 4 type gig), you can get away with a lot less by storing clothes at your hotel.

I'm a big fan of using Eagle Creek 18" folders for packing shirts. At 6 days, I can't do only carry on, I'm not a small size and it just won't all fit. At that point, I'm not using a garment bag, I'm using a RedOxx Beanos 5.5 with two Eagle Creeks on the top and bottom and the suits carefully folded in the middle. I spent years with a Boyt large garment bag designed to take a week on the road, and the RedOxx is so much better at keeping everything reasonably neat.