Cameras like the new Panasonic 4K GH4 need Speed Class 3 cards like the Kingston Digital Kingston Digital 64GB SDHC UHS-I Speed Class 3 Flash Card (SDA3/64GB ) :
http://www.amazon.com/dp/B00I3BQJNA/?tag=tec06d-20
The KINGMAX PRO Extreme SDXC/SDHC is a Speed Class 3 card...