Just my experience, but at multiple companies, which are in the 50-70 employees range, their C# codebases were over 1 million LOC and I didn't get the feeling that they were exceptionally large or doing anything significantly different. I would put 1 million LOC as "medium enterprise . NET" which would place 100k in the small or possibly medium sized if there was significantly more LOC in another language that is part of the project that you aren't counting (eg. different web front-end).