Many of my mp3s are on a file server. Network speed is 10 megabit (approx 1 megabyte per sec). I’ve noticed that changing the ID3v2 tags on such files is quite slow.
E.g. it takes several minutes to copy the ID3v1 tags to the ID3v2 tags on 10 files. This seems a bit slow. Even if every file has to be entirely read and rewritten, that’s 10 files x 4 MB / file x 2 = 80 MB, or 80 seconds. Still a lot, but the actual performance seems slower than that.