If the Big 4 means those 4 players who are currently way above all other players, you just have to ask whether the gap between 4 & 5 is much bigger than the gap between 3 & 4. In my opinion, it is. There are 4 players genuinely competing regularly for slam titles. Nobody else is. There were grounds for hesitation about Murray before he won the U.S. Open since it seemed he might be a hopeless choker in slam finals and therefore not a real competitor for a title despite consistently making the last 4, but his U.S. Open title has put paid to that.
Sensible post as usual. Gamewise we all know Murray is up there. He can regularly beat the other Top 3 and he's miles ahead of those ones below him. His achievements pale in comparison to Fedole, but he has time.