I think the second tier you mentioned there bel is exactly that, the second tier. Nadal and Federer have played a ridiculous amount of tennis compared to some of the others you have mentioned and when push comes to shove during the major events (wimbeldon, french, australia and US) those two always end up dominating the events.
Now, I'd say Djokovic is next to take that BIG step. He had some really good matches this year and on the hardcourt he's an unbelievable player and quickly becoming one of my favourites. Simon, Tsonga and Murray are there and will win their fair share but for at least one more tennis season federer will be amongst the top and then slowly slide down. I think Nadal is the next real thing.