To anyone in the future interested in this, I did some very basic testing of this by creating a user share with a few files in and excluding every other share, then doing a build in order to find out which was fastest on my processor.
Interestingly it doesn't seem like any of them are multi-core optimised (and I guess the build only does one file at a time, at least if they're all on one disk). I got 100% CPU load on one core of my processor whichever algorithm I used. At the end, the build gives you an average speed. I ran all the tests a couple of times with all different files and this is what I got:
SHA1: Was around the 90 MB/s mark (unfortunately can't remember the exact results)
BLAKE2: 93 MB/s
MD5: 323 MB/s
So if anyone wants to install this plugin and their primary concern is speed, at least on the C2750 8 core atom, MD5 is by far the fastest to use. I find it crazy that BLAKE2, which is supposed to be the fastest, is less than a third of the speed of MD5, but this may well just be a quirk of the C2750 processor.