Yes, you can use a 64GB SD card with the Z10. I got this one off of Amazon in my Z10... Amazon.com: SanDisk Ultra 64 GB MicroSDXC Class 10 UHS-1 Memory Card with Adapter (SDSDQU-064G-AFFP-A): Electronics
You just have to format the card by going to storage and access settings before the Z10 will recognize it.
I have this SD Extreme 64GB SDXC Class10. I appreciate your reminder on formatting. Your contribution to the BB World is well noted.