I have an Apple Samsung 256 GB SSUBX SSD which when installed in a 13" MacBook Pro Retina 2014 delivers 1,300-1,450 MB/s Read-Write, whereas when installed in newer 15" MacBook Pro Retina 2015 only provides 650-750 MB/s (both measured with Black Magic Design Disk Speed Test).
Makes somehow no sense to me... Ideas?