What is the Elo of the Mac Book chess engine at top strength?
The Mac chess app is based on the Sjeng engine.

A page on the Sjeng website says:


  Sjeng is probably a bit weaker in bughouse than it is in crazyhouse.
  Most Sjeng's on the FICS have a rating of about 2000 points in
  bughouse, with a top of over 2200 points.
  
  For standard chess, Sjeng's rating is probably about 2450 ELO [sic]. In
  suicide and losers chess Sjeng beats all but the very best humans, and
  will beat non-specialized programs easily.


So, according to the makers of the engine Apple uses, the Elo is around 2450 in standard mode.