If you are experiencing unusually slow performance while running the Guild Wars 2 Mac Beta client on a MacBook Pro with Retina display, be sure that your operating system is fully updated.
If you continue to have problems, try resetting the System Management Controller (SMC). Complete instructions for doing this can be found in this Apple Support knowledge base article:
http://support.apple.com/kb/HT3964
The problem is known to recur, and the SMC reset will need to be performed each time you encounter the issue.
It should also be noted that the performance issue can appear on systems running under Windows. An SMC reset will also be needed if you encounter the problem while playing the Guild Wars 2 PC client under a Windows Boot Camp partition on a MacBook with Retina display.