I don't remember which one it was (I spent loooooads of time soloing quite a few of them) ,but... I finished a nightfall one night and found out a buddy of mine had been keeping tabs on me while I was running it. Boss goes down and I'm absolutely elated (and worn out ;) ). A couple minutes later I get a message from him... "Three and a half HOURS!?!?!?! YOU ARE INSANE!!!!" Those were the days. :)