Performance parity on which axis? For which use case?
Talking generally about "network performance" is approximately as useful as talking generally about "engine performance". Just like it makes no sense to compare a weed-eater engine to a locomotive diesel without talking about use case and desired outcomes, it makes no sense to compare "performance of FreeBSD network stack" and "Linux network stack" without understanding the role those systems will be playing in the network.
Depending on context, FreeBSD, Linux or various userland stacks can be a great, average, or terrible choices.
Linux is a networking swiss army knife (or maybe a dremmel). It can do a lot of stuff reasonably well. It has all sorts of knobs and levers, so you can often configure it to do really weird stuff. I tend to reach for it first to understand the shape of a problem/solution.
BSD is fantastic for a lot of server applications, particularly single tenant high throughput ones like mail servers, dedicated app servers, etc. A great series of case studies have come out of Netflix on this (google for "800Gbps on freebsd netflix" for example - every iteration of that presentation is fantastic and usually discussed here at least once, and Drew G. shows up in comments and answers questions).
It's also pretty nice for firewalling/routing small and medium networks - (opn|pf)sense are both great systems for this built on FreeBSD (apologies for the drama injection this may cause below).
One of the reasons I reach for linux first unless I already know the scope and shape of the problem is that the entire "userland vs kernel" distinction is much blurrier there. Linux allows you to pass some or all traffic to userland at various points in the stack and in various ways, and inject code at the kernel level via ebpf, leading to a lot of hybrid solutions - this is nice in middleboxes where you want some dynamism and control, particularly in multi-tenant networks (and thats the space my work is in, so it's what I know best)
Please bear in mind that these are my opinions and uses/takes on the tools. Just like with programming there's a certain amount of "art" (or maybe "craft") to this, and other folks will have different (but likely just a valid) views - there's a lot of ways to do anything in networking.
Talking generally about "network performance" is approximately as useful as talking generally about "engine performance". Just like it makes no sense to compare a weed-eater engine to a locomotive diesel without talking about use case and desired outcomes, it makes no sense to compare "performance of FreeBSD network stack" and "Linux network stack" without understanding the role those systems will be playing in the network.
Depending on context, FreeBSD, Linux or various userland stacks can be a great, average, or terrible choices.