Otherwise, for this Transcend card, sequential speeds in benchmark 80 MB / s read, 40MB / s write.
HOWEVER, it is fine benchmarks, but in life every day, that is to say continuous shooting, HD video and transfer to the PC USB3, performance is a class FLUSH 10 UHS-I entry (between 17/24 MB / s write and between 25/30 MB / s read). So I see no difference between a daily and a 300x card to 600x.