Prepping for GH4 arrival - here are some testing results of Transcend SD cards with the GH4.
"Bottom line: If you don’t shoot above 100mbps, you probably don’t need to go out and buy a stack of U3 cards for the GH4. 3X faster offload times do make U3 cards a worthy upgrade though."
http://suggestionofmotion.com/blog/panasonic-gh4-memory-card-testing/