Murray has won just one set of Federer in slams including AO so...
Neither Federer nor Murray are the same players they were in 2010. Things have moved on. To me Fed is the most vulnerable at slams to an upset - Murray's been very consistent since US Open 2010 shock loss to Wawrinka (lost to Fed, Nadal, Djokovic and once to Ferrer at RG only) whilst Fed has lost to Berdych twice and Tsonga as well as the usual Rafole combo. [Sure Nadal had the worst upset at Wimbledon but for now it seems like an anomaly amongst his other slam results of the last 2 years.]
No way saying that Fed is an easy pass, just that in best of 5, seven matches, 2 weeks, Fed's lost a step understandably. From here on out apart from RG I see Federer being the more preferable opponent rather than Murray in a slam semi. Murray can make you stay out there for 5 hours killing yourself. Fed needs to go to God-mode (like he did in the Wimby final) or will usually shank himself out of the match.
Just my impression. Murray could bomb tomorrow and in the Aus Open to prove that totally wrong. Who knows.