Fed is now officially #5 and he has surpassed Murray.
If Fed wins IW, he becomes #4 instantaneously.
Even if he does not win IW, as Fed has 0 points to defend in Miami
and Ferrer (the current #4) has 600 points to defend (he was a finalist
last year), he is almost sure to become #4 by the end of Miami.
However, beware Fed Fans. Assuming he maintains this spot
(which is not difficult to do so), he will get #4 seeding in FO.
But, as all of you know Wimbledon seeding is a different story.
Even though Fed may have already surpassed Murray, Murray
will have a tremendous edge over Federer in the seeding formula
as he won it last year (and a finalist the year before) and Fed
faltered early there.
So, in order to ensure that he can get #4 seeding, he needs
to widen the gap between him and Murray. That looks highly possible
as Murray has to defend 1000 points in Miami and the way he
is playing currently does not give any indication that he will
get more than 100 points. But, it is going to be a tight race
between Fed and Murray in the end for the #4 seed in Wimbledon.