Something to consider is the MTU size or what are called Jumbo Frames. Full-Duplex and TOE are two other things to look at.
I'm running FreeNAS 8.3.1 with exporting iSCSI disks back to linux boxes running virtual machines off the mounts that are pretty i/o intensive. Setting the frame size larger than the default 1500 had a dramatic impact on performance and throughput. This has to be set on both the client and server side or it doesn't take effect.
FreeNAS has some nice graphs to allow figuring out where your bottlenecks are on the system information tab.
Oh and a free heads up, changing the MTU size is part art and part science. Drivers in FreeBSD, Linux and Windows are unreliable in what sizes are allowed. You may have to dig into the driver documentation or experiment to get the sizes that are acceptable. Also, lowest value is the default for the entire path.
On linux or freebsd/freenas:
ifconfig -a | grep -i mtu
ifconfig eth0 mtu 9122 up
ifconfig em0 mtu 9122
On windows right-click the NIC in device manager and look in the properties of the NIC driver. MTU or Jumbo Frame or Framesize may be the name of the setting for your driver. The default value is usually 1500.
To test the route MTU values from Linux:
route get <ipaddr>
Some notes will mentioned hardwiring full-duplex but any modern switch will deal with this quickly and not be a problem. I did not see any issues with duplexing on modern hardware.
For my iSCSI usage, the blocksize of the exported volume was important to be larger and I set it to 4096 for the virtual device. Pay attention to block sizes of the underlying exported volume as those also have impact on performance. That may not impact your SMB exports.
One last question, if your 10Gb NIC TOE (TCP Offload Enabled) enabled or hardware accelerated?
TOE is the network card equivalent of a GPU from a graphic card along with something like DMA (Direct Memory Access) used by old style hard drive controllers. It allows for offloading the work of the TCP/IP stack to the NIC instead of running it through motherboard front side bus and CPU which are bottle necks for data being processed at this speed.
In order for what you are asking to work you will need your 10Gbps cards to have TOE (hardware acceleration) enabled in the OS and drivers. If you have already TOE enabled, then ignore this part of the response.