Nada...see my thread. That's an easy fit.
20 w/ 70-200 attached in middle. 17-50 on one side and 100 on top. 420EX can go in the middle as well, just remove one flap and use the 70-200 in that area, the 420 goes behind the other. Now you still have the "hidden pockets", the front pocket, and a whole side left to use.
What he means is the 17-50 and the 100 on the right side, one in the back and one in the front. You can also squeeze your flash in the middle with the camera and yes, then you still have a whole right side. If you have short lenses, such as the 15mm, then you can actually place them on top of one another... This should be an easy fit. I have room to spare and you see what's in mine...(And the 85L is a beast!)