One of the fact that surfaces from the book Just for Fun: The Story of an Accidental Revolutionary is that Linus wrote the code for Linux in ~15 months and it was ~15K LOC. I usually take that as gold standard for productivity of brilliant programmers. Note that as per the book, he almost exclusively spent entire time writing code during these months (he would put down the curtains if it was a rare sunny day outside and skip showers and just about any events so almost all he does is write code).