I have another book that is a take on a similar theme. It's called Replay by Ken Grimwood and won the 1988 World Fantasy Award. Basically about a guy who is in a time loop. But on one of his loops LHO does not kill JFK, but someone else does! He finds as his replays go on that he cannot change any major events that have occurred in the world. It's a very good book.
And yes, I think The Dead Zone is SK's best book. A big call, I know, but his characterisations are so marvellous - what I like best about his novels - you can see how Johnny's thoughts are slowly changed and how he justifies himself. I like Rose Madder for the same reasons - his insights into the inner workings of our psyches is terrific.