Nick, I'm in the same situation as you. I keep most of my bigger flies in Plano type boxes, but when I say bigger flies, some of mine are 8 inches long or longer. I don't have a problem with them jumbling around however, because the boxes are stuffed so full, they can't move around much!
I'm not that impressed with the Cliff's boxes, particularly for the price, but I know many use them.
I just placed an order for 3 fly boxes, smaller than the Cliff's, but hopefully large enough to at least carry a couple dozen flies. If they're of sufficient size, that will be my solution. I would rather carry a couple of smaller boxes, than one big one. I won't know until they arrive.
I also have 2 Plano boxes I use when boat fishing. I'm not sure they're even still made, but they're generally shaped like the Cliff's with a handle on one side & made so they can be attached together. However, they're compartmented and don't have any foam in them. So far, they've been the best solution I've found for carrying a lot of big flies. I use one box for subsurface & the other has both subsurface & topwater flies in it.
BTW, many of my bass flies also are the same flies I use for Striped bass and I have a lot of flies!
Here's my boat boxes: