I had an early Waterford AHH size 65. It maxed out at 38x700c tyres. In fact, I ended up parting ways with it because of that. I did really try to get Bruce Gordon Rock n Roads to fit, but it wasn't even close. I think I would have kept to if could have.
The problem was the seats stays weren't dimpled. So it might have just been that particular frame, though I don't really know. I did inquire with a frame builder about dimpling them, but was told it was too close to the bridge that it would probably ruin the frames structural integrity.