Are the hosts actually connected with 10Gb links? Several hypervisors including Hyper-V report 10Gb nics on the guest-os which doesn't necessarily mean they actually have a 10Gb link. Having said that, I am currently planning a datacenter move. Our main datacenter has a few HP DL360 G9 machines, each with 2 Xeon 2950V3 CPU's, some pretty neat and fast 10core machines, so a total of 20 cores (for what that matters). We are running pfSense (on Hyper-V) on those boxes, and it never passed 60MB/sec, about 500Mbps.
In our new datacenter though I've mounted a spare Cisco 3750 switch and a Xeon L5520 based machine, so even one generation before your L56xx host. With the exact same pfSense setup on Hyper-V as well this much older machine reaches linespeed and I can do a 115MBps, so about 1Gbps down and up. Note that I am running pfSense on Hyper-V 2012R2, which isn't even the best hypervisor for it at all. Now this difference might be the line in our current datacenter, but it might as well be some other issue. In any case, the rather similar L5520 based machine can actually do 1Gbps routing with no issues at all in my setup. No specific tweaks done at all.