Haven't tried this myself but using USB 3.0 ports and devices should improve things immensely. Another option is to use something the 'old' floppy based installs did, boot from the device, load everything into memory disks and run from there. But this does require a fair amount of available RAM.FreeBSD on USB memory stick runs stable, but very (VERY!) slow, and also suffers from very long lags all the time.
I run FreeBSD off a USB stick exclusively for my NAS without any performance or stability issues at all and no requirement for labels.
Of course you do not need labels if you plug it into the same machine / same configuration all the time...
Googling around, I found lots of threads from people complaining about very poor USB performance in FreeBSD. But there was never a solution.
It seems that either you're lucky, or you're not. I am not. Just as an example, I run Linux and FreeBSD on the same stick (multiboot). Installing the MATE Desktop on a basic Linux system took 45 Minutes, doing the same on a basic FreeBSD system took 14 hours (!).
That's my (and many others) experience.
Maybe it depends on the specific machine's chip, maybe on the USB hardware itself, maybe it's a problem with USB 2.0 only (that's all I have). Nobody seems to know. I would appreciate any solution.