I personally feel like at this level of traffic, A entry level of linux server (like dell r210) with adequate domain knowledge is the best combination. It would happily do most stuff you throw at it, if you know how to use it. Entry level hardware solution tries to hide details from user, because they want to target clueless consumers, but it sounds like a PITA for me. If I had to learn new stuff, i better spend my time on some real industrial stuff (like m7i/m10i ).
General purpose servers are usually good performers, but more network-centric x86 hardware is available, such as: http://www.serveru.us/en/ And running VyOS on those servers, although requiring to learn some new stuff, might prove handy due to nice features in device management. Forgetting to add command lines to /etc/rc.d start-up files is a common cause for issues using general purpose operating systems, and you will its CLI very close to the real industrial stuff. Rubens