These Samsung cards should be great for the GH4 as they have high data rates.
http://adorama.evyy.net/c/60445/51926/1036?u=http://www.adorama.com/ISGMBSGBG3P.html
Samsung ” 3 PACK ” 32GB SDHC Pro UHS-1 Class 10 Memory Card, Upto 80MB/s Read, Upto 40MB/s Write
Regular Price: $89.85 Sale: $49.95 + free shipping and Free Card Reader
http://adorama.evyy.net/c/60445/51926/1036?u=http://www.adorama.com/ISGMBSGCG3P.html
Samsung ” 3 PACK ” 64GB SDHC Pro UHS-1 Class 10 Memory Card, Upto 80MB/s Read, Upto 40MB/s Write Speed
Regular Price $174.00 Sale: $99.99 + free shipping and Free Card Reader