I purchased a few of these elsewhere, but B&H now has the Sandisk Extreme UHS-I Speed Class 3 SDHC Memory Card (Class 10) 65 MB/s cards available now. These are not fast enough for the BlackMagic Pocket Cinema RAW, but a great option for your GH4 4K or 1080p 200MB/s files if you want to stick with name brand.
There's currently discounts going (today only) for various types of Sandisk Media. Sucks because I just paid for a 32GB MicroSD Card for my new Samsung Galaxy IV cellphone and GoPro Hero3. I could have used these deals a few days ago. Check it out via B&H and remember it's for today only (found here)
Sandisk Media One Day Sale