I agree with Jim. The Think Tank doesn't seem to different in size than Click's Pro Elite bag, which has twice the storage space of my bag. I fit my camera body, a 100-300, a stout 150 macro, and another stout 18-70 (Sigma lenses are built like tanks, bulky and heavy) and even have room for one more medium sized lens or two small ones.

My local photo store let my take my gear in and try out a bunch of different ones so I knew the space would be correct, maybe yours does too.