The Transcend 64GB Class 10 UHS-I 600x card offers write speeds up to 40MB/s and read speeds up to 80MB/s. Check it out here on Amazon.
The Transcend 64GB MicroSDXC Class10 UHS-I card offers read/write speeds up to 45MB/s. Check it out here on Amazon.
Class 10 cards deliver on speed for HD video capture, which goes along with the size advantage of the SDXC spec. For more details on what all the classes and card specs mean, check out my resource article Demystifying SD Cards.