Two things:
First: It sounds like you've misconfigured your network with the explanation you provided with the CT. No clue what you did wrong since there's so many ways to break networking.
Second: Why would you put 2 PCI NICs on LAGG? Do you realize that the PCI bus cannot even keep up with a single Gigabit NIC's throughput? Not sure what value I'm seeing aside from redundancy, which many will argue is not truly that high of a priority if you are using PCI to begin with.
OK.. 3 things:
With the kind of throughput you are hoping to get with 3 NICs on your system, why oh why would you use a system with only 8GB of RAM? Sounds to me like you really aren't recognizing the fact that you've got other bottlenecks all over the place slowing you down. Just from what I've read, your CPU, your NICs in PCI, your Atheros, and your small amount of RAM all are potential bottlenecks that are definitely limiting you in various fashions. I'd look at just replacing the whole system with something newer, and with Intel built-in.