For many people 64gb cards work a treat on others the phone wont detect the card.
It depends on your current Rom and on the brand of your Micro SD card (For example i heard that Sandisk 64 Micro SD card work with XSP )
If I helped spam that "Thanks" button
Phone :Xperia SP
Android Version : 4.3
Kernel:Stock .266 Kernel with CWM rootable by Doomlord