The Lowepro Flipside 300 camera bag is an excellent choice, I pack my 5D Mark II with a 70-200mm Canon lens (reversed lens hood) attached. I also pack a Canon 28-135mm lens and my Canon 580EXII flash and with a dome for the flash, sync cord, small camera books, batteries & charger. I use my Lowepro Flipside 200 when shooting quick jobs, I pack the 5D Mark II with either lens in this bag.
I think it looks perfect, but I need to make sure that I can get the camera with 10.1" lens attached to fit. I'd need about 14" and I think with the top bag removed it would work. Thanks