A 64-bit client is now available for use with the 4.3.2 PTR. You can download it at the link below, unzip it into your PTR directory, and then run the executable to test it.

• The 64-bit client is being distributed separately from the PTR as it is not yet supported for use with World of Warcraft.
• This can only be used with the 4.3.2 PTR, it is not to be used with the live version of the game.
• A Mac version is not available yet, though we are working on one and plan for it to be available in the near future.
• The game’s built in voice chat does not currently work in the 64-bit client.

link

If you encounter any issues while using the 64-bit version, please report your findings in the PTR bug report forum (http://us.battle.net/wow/en/forum/2359401/), and return to using the 32-bit executable.