I set the MTU to its max (just over 9000 on the intel, heh), but that didn't make a difference. The one thing that did move the needle was overclocking the CPU to 2.147 GHz (from base 1.5 GHz clock), and that got me to 3.4 Gbps. So it seems to be a CPU constraint at this point.
Oh shoot, completely forgot to do that, as I was testing a few things one after the other and it slipped my mind. I'll have to try and see if I can get a little more out.