I use an Incase Pro DSLR Sling pack - http://goincase.com/shop/incase-dslr-pro-slingpack
If you fancy 2 straps (which it seems you do) they also have that - http://goincase.com/shop/incase-dslr-pro-pack#color/129/view/8
which seems like it has a different configuration than mine, but similar capabilities.
I really enjoy that with 1 strap I can swing the bag around to the front and grab gear on the fly (it also makes a useable 'tabletop' that way). It's actually
as functional as they advertise in that respect.
It carries all that you listed and probably more, and yes it ends up weighing a ton, but it's manageable. It's very capable and fashionable when traveling. (I like to think it just looks like a backpack, and not necessarily like $8k worth of camera gear.) When forced to pack it all it can hold
a 5D3 attached to 70-200/2.8,
a 5Dc attached to a small prime (40/2.8 pancake usually)
2 Battery Chargers
I can even find a way to arrange a 2x extender in there too if I'm feeling dumb.
and of course all the extras (and it has a strap for a tripod). And again, all that is ridiculously heavy, but possible.
I would imagine the 2-strap is a similar size. the pictures certainly seem to suggest it.
Oh and lastly - build quality: Incase stuff is built fantastically. Soft shell on the outside, so it's no tough case but it will certainly last.
- EDIT -
Sorry, a double take made me reconsider my assumption of "all that you listed and probably more"
- another prime lens or 2
in combo with
- 2 yongnuo speedlights
- at least one
2.5" external HDD …
Depending on the size of those drives.. I seriously don't know if anything not on wheels can handle all of that.