[QUOTE=Superbaldguy;1464]The F6 looks to be sort of a cross between the larger F1-X and maybe the F3, but it is that different from the original F2 in many respects?[/QUOTE]
I have one of each. The F6 is pretty much an F2 with no side pockets and just a bit less volume in the main compartment. Length and width are just a bit shorter, and height is about 1.5 inches shorter. The one zippered front pocket holds a lot, and makes up for not having the side pockets to an extent. The F2 will hold my 70-200 vertically with hood on and reversed (I have the wide angle 4 pocket insert) without the lid bulging. I can honestly fit about the same amount of gear in both bag's main compartments, but the F2 is comfortably packed with room for a few extras, while the F6 would be stretched tight. This makes the F2 easier to work out of IMHO. I use the F6 when I am carrying two lenses, generally my 135 f2, and 24-70 f2.8 along with my ungripped 40D. If I'm taking the 1D MK3 and / or the 70-200 f/2.8 with me, the F6 stays home.