Before ever venturing in performance comparison we need to define where, when, under what circumstances and for what purpose. Usually benchs are carried out on powerful modern workstation and servers, and focus on compiling databases/langs, I/O scheduling, garbage collection, executing shell/java/go scripts, audio/video encoding, packet filtering, write speed, backup, uncompressing. Then there's special performance benchs focusing on scalbility o HCI envs, or those regarding CDNs and focusing on network stack, or also VMs performance on hypervisors guests for cloud providers
Benchs usually do not focus on low-end hardware, laptops, tablets, embedded devices, gaming, graphic designing, multimedia streaming, text processing, download speed, etc...
When we speak about current DBSD performance benefits we're referring to medium-to-large servers and powerful workstation equipped with 128GB+ DDR4 ECC RAM, multiple high-end amd64 CPUs (i5-i9, 32+ cores), multiple large HAMMER2 -formatted M.2/NvMe SSDs, 256GB+ SSD dedicated to SwapCache.
HAMMER(2) on a <1 TB HDD without 8+GB RAM and a dedicated SwapCache is going to be a performance/battery killer and will rather slow down your PC compared to other BSDs.
You also have to keep in mind that other OSs, often with a larger manpower and more cospicous fincements at hand, target performance as one of their primary goal too. This includes Linux, Solaris and FreeBSD. Overall, Linux at the current state is the top one challenger in the performance race. Under some circumstances, Solaris can still beat Linux in terms of vertical scalability. FreeBSD lags behind a little bit, but again, its TCP/IP stack has been show to still perform slightly better than Linux,especially in regard of PF+ALTQ vs Netfilter.
In spite of its focus on performance, DBSD is not a winner here: all benchs reveal it barely keeps up with FreeBSD, generally performing a little worse than the latter in most scenarios;
A completely different argumentation involves performance on limited specs, old hardware, legacy ISAs, embedded devices. Here is hard to find something performing better than NetBSD, even though, again, Linux can catch up with NetBSD in most situation. NetBSD runs well on 8MB RAM, on limited CPUs like Amigas' m68k, and flies on older hardware. It's tuned to be essential, mimimalist and as little resource-hungry as possible. But, even here, our talk is pretty much relative and debatable. if we move onto 8bit CPUs, e.g. Z80, 8080, both Linux and NetBSD won't be even able to boot on them; those ISAs require OSs capable of running on <128 KB RAM, like Sinclair BASIC or CP/M respectively.
To sum up, if you want performance on BSD, my recommendation is:
With 8GB+ DR3/4 RAM, 3.x+ GHz CPU / 4+ cores, 500 GB+ storage, choose FreeBSD on ZFS or DragonflyBSD on HAMMER2. Keep in mind HAMMER2 is desifned to run on SSDs; also, I'd pick DBSD only if I had a spare SSD to dedicate to SwapCache
with everything below those specs, I'd pick NetBSD (or a lightweight Linux distro, or FreeBSD on UFS as third choice).
OpenBSD will always be slowest, regardless of hardware
