I actually think Murray has a greater chance of achieving CGS than Stan, even though Stan needs only one more and Murray needs two more.
1. In AO Andy has reached the finals multiple times. You keep knocking the door and the door will eventually open (especially if the doorkeeper takes his eyes off to look at women).
2. Andy was generally considered to have a clay problem. In view of this many people also said he will never achieve #1 ranking, as it includes clay points. However, Andy proved them wrong, did well on clay last year (winning a Masters and reaching the final at RG). So, there is a reasonable chance that he will improvise on the act and get his hands on Coupe de Mousquetaires (especially considering KOC has abdicated his throne).
Stan may have only Wimbledon left, but he is never going to win that. Look at his record at Wimbledon. He has never done well there. Further, Stan's play relies on powerful shots in which he takes a huge cut for which you need time. Grass takes away the time. Hence, based on playing style also Stan has not much chance. Stan has his lowest win percentage in Wimbledon at 60% with a record of 18-12. He had played there 12 times, losing in R1 5 times, R2 twice, R3 once and R4 twice. His highest achievement there is to reach QF twice. But after doing that, he again lost in R1 this year.
Posters here seem to think just because Stan needs only one more and Andy needs two more, So Stan has more likelihood of accomplishing it. Based on their style of play and also based on their results on missing GSs, I think Andy's chances of accomplishing it are substantially higher than that of Stan.