Thanks John. The 550 and SB900 are just a bit bigger than the 580EX. The gripped D700 bodies are the size of a 1 series too.
Looking at your photos i'm not sure how everything will fit for me. I like to keep at least one body with a lens on ready to go, two if possible, and I need to be able to chuck things in quite quickly when moving locations. The only disadvantage of the security seems to be it's not great for travel, which really isn't a big requirement, just a "nice to have". Having a strap so my assistant can easily carry the bag around fields could be handy too, I shoot in quite a few rural locations.