Absolutly stay away from cards with this chipset as on the X540. You wont reach more then 2Gbit/s Troughput on them, and nothing will help except installing ESXi on the host and then pfsense on top. I made my head out with that cards with days trying to debug slow troughput with pfsense trying everything i could find, consulting with people on the pfsense ircchannel and alot more.
we finally fixed the issue by replacing the x540 cards with cards that have a qlogic chipset.