Silver Age Superman probably remembers his dealing with the Hulk, which is why he replies, "They surrender" to the question, "What happens when the Unstoppable Force Meets Immovable Object." That's precisely what happened in that crossover.
Lex realizing that life is interconnected on a universal level, in defiance of entropy is why Superman has a Thou Shalt Not Kill philosophy - everytime someone dies, that universal bio-web becomes weaker, weakening everything, including life itself. Everything is connected indeed.
During his last act of heroism, Superman flies off at sub-sonic speed, since any faster would knock everyone down — but notice when he reaches the end of Earth's atmosphere, he flies fast with a burst of light. That's Superman breaking the luminal barrier, since he's flying faster than the speed of light; he takes far less than 8 minutes to reach the Sun.
Many people see Doomsday Jimmy beating Superman as a Moment of Awesome. However, that may only have been possible because Superman was rapidly being inverted from the powerful, intelligent person he normally is by the time Jimmy turned up to fight him. Given what happened in the main continuity, if Superman's handicap had not had some time to work on him, it might well have been that Jimmy would have been able to minimize the damage, but Supes would have beaten him to death in the process.
Something seems odd when Batman (the world's greatest detective) doesn't make a single appearance in this story. Not even for a cameo, or to comfort one of his closest friends (in most continuities at least) as he's dying.
