The local web server I built a few months ago uses a Xeon, the E3-1220v3. To my knowledge that is enterprise grade (and one of the “slowest” Xeon versions on the market).
It’s made for entry-level business class server applications. The hardware for my rig was peer reviewed by @elberet (bless him for putting up with my newbie antics). If he approved my choice to use the Xeon, then I think it will perform well for Discourse.
That, and as Jeff mentioned, it is ~2 years old (2013), we’ll above the 2011 floor stated.