I polished my parallel grep version. When I started it in 2012, multicore + SSD setups were not that common. Today, lot of storage is on flash or SSD, so you can benefit from parallel grepping by a factor of 3 or more (depending on amount of CPU cores). Just check out the link; it will also contain some timed runs to underline the statements. I also noticed that my previous git singing key expired, so I will need to resign the repos with my new GPG key (already uploaded) over time.

Update: I added a new branch to the repo to again double the speed by an dedicated nftw() + readdir() implementation thats parallelized and recursive at the same time! If you enjoy brainfucks, give it a try!