Mission accomplished. We have beaten the game, and it can now go on the shelf, a conquered trophy.
Sometime late last night we started experiencing some really obnoxious framerate issues, about halfway through the game. A bit of research revealed the culprit to be the patch for the game. We removed the patch, chose not to re-download it, and all was well from there.
All in all, an excellent game. Not quite as “scary” as we were expecting it might be, but the atmosphere was amazing.