yup, for comparison, same file as above using all the threads (32) on my system, I get about 45ms with fully parallel permitted b3. It does run into diminishing returns fairly quickly though; unsurprisingly no improvements in perf using hyperthreading, but also improvements drop off pretty fast with more cores.
b3sum --num-threads 16 /tmp/rand_1G ran
1.01 ± 0.02 times faster than b3sum --num-threads 15 /tmp/rand_1G
1.01 ± 0.02 times faster than b3sum --num-threads 14 /tmp/rand_1G
1.03 ± 0.02 times faster than b3sum --num-threads 13 /tmp/rand_1G
1.04 ± 0.02 times faster than b3sum --num-threads 12 /tmp/rand_1G
1.07 ± 0.02 times faster than b3sum --num-threads 11 /tmp/rand_1G
1.10 ± 0.02 times faster than b3sum --num-threads 10 /tmp/rand_1G
1.13 ± 0.02 times faster than b3sum --num-threads 9 /tmp/rand_1G
1.20 ± 0.03 times faster than b3sum --num-threads 8 /tmp/rand_1G
1.27 ± 0.03 times faster than b3sum --num-threads 7 /tmp/rand_1G
1.37 ± 0.02 times faster than b3sum --num-threads 6 /tmp/rand_1G
1.53 ± 0.05 times faster than b3sum --num-threads 5 /tmp/rand_1G
1.72 ± 0.03 times faster than b3sum --num-threads 4 /tmp/rand_1G
2.10 ± 0.04 times faster than b3sum --num-threads 3 /tmp/rand_1G
2.84 ± 0.06 times faster than b3sum --num-threads 2 /tmp/rand_1G
5.03 ± 0.12 times faster than b3sum --num-threads 1 /tmp/rand_1G