According to Boswell's Life of Johnson, the last words he spoke were "God bless you, my dear" addressed to, Miss Morris, the daughter of a friend of his. Not very memorable perhaps, but Boswell must be the best authority there is.
Thanks, everyone. I like the 'z' solution, but... And, the Boswell version isn't one of the four options. I'm going for 'Iam moriturus', 'I who am about to die'.