Hi Tom,
There is a bit of a "history" with support (or lack of) for the FreeBSD OS. Mellanox has primarily been focused on Linux OS support but due to customer and industry demand, Mellanox is in the process of porting our latest and greatest Linux MLNX_OFED driver (which includes the Ethernet driver module) to FreeBSD10 with a goal of achieving the same performance (in both 10GbE and 40GbE modes) as in Linux. The GA (general availability) date for this FreeBSD10 driver is currently scheduled for Aug.30th. The current FreeBSD10 Ethernet driver which is available was only optimized for 10GbE mode and not 40GbE mode. Hope this helps? Thanks.
Branko.