I have that beat
I have encountered 20+ GB PSTs in recent months. Some of the people I support have saved every email they have sent or received for the last 10+ years in a single PST. Every time I encounter this breed of user, I encourage them to split their archives into smaller chunks and to disconnect older PSTs that are not needed on a daily basis. You would think I had horns the way some of them look at me when I suggest that.