I think the size of the bag is only one component to an effective solution. I think changing the way one carries gear also has a significant impact. No specific gear back recommendation here, but a few comments...
It's the damn 35' cables for the other channels that are the killer.
FWIW, I've found the best way to schlep cables is not
inside the bag, but rather attached to the outside of the bag. I simply loop my SoniCase should strap through the center of each cable coil and they dangle off the top edge of the bag.
And then there are headphones, clamps and accessories and on and on.
What headphones? When I used to carry my Sony MDR-7605, I gave up trying to stuff them inside the bag. Instead, I tossed them in a small pouch that I again hung off the outside of the bag. Now, I carry Etymotic ER-6s and they easily fit inside the bag.
What clamps? I've found the Windtech "C"-Type clamps the most compact and flexible of the ones I've used. 'Course, I also carry a SuperClamp, too, which gets a bit bulky.
Couple additional things I've done (or do sometimes) to reduce the size of stuff I'm carrying:
- carrying my 414 shockmounts attached to my mic stand, sometimes; saves a LOT of room inside the bag for other stuff, and after folding up the shockmounts doesn't make the stand all -that- much bigger
- replace the hard plastic, foam-lined case (talk about bulky) for my 414s and use padded camera lens pouches instead; while they won't offer protection if my bag gets run over by a car, they - along with the padded SoniCase - will serve their purpose if I drop my bag (the accident most likely to occur that may damage my gear)
FWIW,
here's a list and pics of what I cram into my 4-shelf SoniCase. For most recordings, I'm now down to just the SoniCase with no accessory pouch (by moving the shockmounts onto the stand). In that new setup, if I added a V3, I'd simply transfer the contents of one shelf to the accessory pouch and slot the V3 in the bag, for a total of SoniCase + 1 accessory pouch.
$0.02