Curse you all for mentioning NICs. A 2 SFP+ port card has fallen into my shopping cart.
I was very tempted to get a 2 port but I figured I might need that money for, you know, food, bog roll, etc.
I ended up getting an Intel X520-DA1 which hopefully will work with the 10Gtek DAC cable. They claim it works with their version of that card, but then they charge twice as much for theirs as I got that one for new off eBay. (I could have gotten a 2 port card for the price of their 1 port)
Reading the Linux kernel module documentation is kinda scary, as it implies by default it blocks all SFP+ modules/DACs that have not been tested which seems kinda silly IMO. I know adding module options isn't hard, but I'm always expecting them not to work.