In the 15 matches that Federer and Murray have played
, neither player has ever had higher success on second serve than on first serve.
It's interesting how Federer has out-aced Roddick in 14 of 21 matches, but he's out-aced Murray only 3 times:
2006 Cincinnati (6-4)
2008 Masters Cup (11-7)
2010 AO final (11-10)
Murray's success on 1st serve against Federer has been very high (partly due to the aces no doubt). In their '08 Dubai match he broke 90% on 1st serve success (something Federer hasn't done in any of their matches).
And yet in their very next match -- the USO final -- Murray's success on 1st serve was a horrid 51%.