World of Goo (90%), Machinarium(90%-95%) and the PC Gaming Alliance (90% for high end titles) have all claimed piracy rates of 90% or above.

Also there seems to be a gap in your reasoning, going DRM free didn't cause the overload on their server, unless you're claiming that going DRM free caused people to pirate it. The huge pile of (previously) DRMed media currently being pirated would beg to differ with you. They did use accounts (or a code per game), so the pirates were unable to log in to the server, but the fact that they were trying to is what was causing the problems (from the update at the end of the article). If they'd had DRM, it would have been cracked, people would have pirated the game, tried to contact the servers and they still would have fallen over.