Thanks that makes sense. Seems to be like you said, Josh, without the queues on different interfaces somehow communicating with each other, they can't shape properly if given access to sort of "overlapping" bandwidth. I might have to look into this a bit more :) I do find it really interesting and confusing trying to understand exactly how TCP works in this kind of situation. I think probably each network will end up getting bandwidth proportional to how many connections it has, and no way to specify "network 1 limit bw to .3k only if other networks are using 1.2k"
I like the idea of using 5 interfaces and pluging one into the other, should be able to do that with a little VLAN switch… which then makes me wonder if you couldn't do that somehow within pfSense using vlans and bridges somehow... have to look into this now...