Which bag ?
 

Hi, I have Canon EOS 5D MKII, 24-105 F4L, 17-40 F4L, spare battery, CF cards and lens blower. What do you suggest ? I thought F8 but maybe F6 better ? I currently have F803 for my M6 and like it's discrete/snug fit when over shoulder. Cheers, Steve:)

Hi Steve,
An F-8 is way too small, an F6 might be pretty tight. An F-2 is probably what you want.

Interiors:
F-8 = 6.5" Wide x 3.5" Deep x 6.5" tall
F-6 = 11.25" Wide x 5.5" Deep x 7" tall
F-2 = 11" Wide x 6.5" Deep x 8.5" tall

I think an F-3x would be good also. I keep my 5D (or 20D, or 1D3) with a couple of lenses in the main compartment of mine and put the flash in one of the side pockets.