Yeah, the French is very unlikely. He did improve on clay quite a bit last year though, he should of beaten Djokovic in Rome, pushed Nadal hard in Monte Carlo before he injured his arm, then made the semis for the first time. I think the other 3 are just too good on clay for him though.
As for Wimbledon, I agree. I think he would beat Federer on the surface these days, Djokovic would be an interesting match up, whilst Nadal has always caused him problems on grass for some reason. Berdych could also be a problem, as he is on any surface for Murray. I don't think Tsonga is too much of a concern though, they've met on grass a few times over the last few years and Murray seems to have that one covered. I also don't believe the pressure is on him as much as it's made out to be, I don't think he feels it that much either. Henman had it for sure, but Murray is a totally different personality and I think he quite likes it. He says he enjoys being able to stay in his own home, which I think helps.
I think the Australian Open or Wimbledon are the most likely. For some reason I don't fancy him at the US Open, there's a big lead up to it with all the North America hard court tournaments and alot of players are usually in good form by then. There are too many contenders for that one to make it a likely place for him to win imo.