Hi I am looking to upgrade the SSD on my MacBookAir7,1 (11") early 2015. I need a 1TB disk. I saw the Transcend JetDrive 820. (speed according to data: read & write 950MB/s) My question, how fast is the "original" ssd that is built in, in my macbook? (cant fidn the info) Is the Transcend slower or faster? thank you.