I'm using a Patriot LX 128GB card and it works fine: http://www.newegg.com/Product/Product.aspx?Item=N82E16820220756 4K is just under 1GB per minute so support for a 128GB card is not trivial. Using a Kenyon Labs KS-2+2 gyro to keep it hand-held steady, important when shooting 4K.
Pro quality at a consumer price; The ultimate accessory to my 4K monitor! Full spectrum of auto and manual controls to rival any pro camera; Complete accessory package; Remote control is nice (camera/gyro in one hand, control in the other)
Just nits; The LCD isn't 4K (but that would be overkill/unnoticable for a 4" display); Hard to see it in direct sun (Duh) and doesn't like polarized sunglasses (Duh again); Eyepiece is also low resolution; Knew this all up front