Insightful post. Murray is an interesting one. There is no way Murray should lose to someone like Nadal on hard, especially at the US open. On grass it should be a 50-50 match up. I will not bother with clay, we know who has the edge. I expect Nadal to continue doing well against the Djoker on clay. On grass and hard I believe Djoker will have the edge. Unlike the other players on the tour Djokovic does not fear Nadal. Had the final not been stopped at the French last year Nadal was all but toast.
With Federer losing steam, the top 4 seems to be destined to become top 3. I don't see #5 to #10 challenging the top 3 consistently in slams. Then the draw becomes a factor. Murray ... I have my money on him this Wimbledon. The way he won the Olympics on grass, I think he should be able to pull it off. He is better than Nole on grass. His mental block against Rafa is worrisome.
As far as the other guys... Del Potro, Berdych, Tsonga ... they are decent but in 3 out of 5 sets match, my money is on top 4. Can Raonic or someone like that step up next year? We shall see.