Assuming UBNT is correct and the device supports line-rate throughput, I don't think there's any reason why FreeBSD couldn't easily support that.
The freebsd-mips mailing list already has a few threads discussing this; if you want to know why the router isn't achieving line-rate speeds "out of the box", you'll probably get the best answer there (and maybe even someone who knows how to fix the problem):
The freebsd-mips mailing list already has a few threads discussing this; if you want to know why the router isn't achieving line-rate speeds "out of the box", you'll probably get the best answer there (and maybe even someone who knows how to fix the problem):
* http://lists.freebsd.org/pipermail/freebsd-mips/2014-January...
* http://lists.freebsd.org/pipermail/freebsd-mips/2014-Februar...
If you don't get a suitable answer there, you can also try freebsd-net:
* http://lists.freebsd.org/pipermail/freebsd-net/