This doesn't exactly answer your question but, both the Realtek 2.5G and Intel 2.5G desktop NICs have had some issues operating at 2.5G speeds. These include weird timeouts, random connectivity drops/reconnects, odd data transfer rate drops when not under load, etc. These have primarily been reported on a lot of the gaming Reddit threads that I follow as the guys there tend to build with the newest hardware and they were all early adopters of these NICs built-in to their new mainboards.My 2c, I would avoid anything right now with either of those 2.5G desktop-class NICs. For a firewall, I'd pay the higher cost and go upmarket to the server grade X550 and then "downclock" it to the 2.5G speed that you want.