I have the Sandisk Extreme Plus 64GB, the Ultra 128GB and Samsung Pro 64GB. Benched all three and the Ultra is definitely the slowest by a good margin. The Sandisk Extreme Plus was slightly quicker on reads than the Samsung (50Mbps read / 40 Mbps write) , but the Samsung was a bit quicker on writes (45Mbps read / 45 Mbps write). The Samsung seemed to be more consistent as well. This was using A1 SD Bench. Not going to swap out cards and run them all again so you'll just have to take my word for it.
Furthermore, Sandisk usually used not only one production line and the speed usually is different.