I would probably get a nic that is 10g but also goes to 5g,2g,etc.
I got this from Amazon and it supports 2.5g. And does work in linux, it should work in pfsense as well, but i will be testing that later this week. I will update later!
I just ordered a r230 to use as a pfsense box to replace my aging r210. I will have that card as my wan from my new Motorola MB8611 with the 2.5g port. And keep my Chelsio 10g card as my lan connection.
(sorry for formatting on mobile)