I have the iMac 5k i5 3.2Ghz Late 2015 and I installed a 256GB PCIe SSD (MZ-JPU256T/0A6). I can only achieve 700Mb/s read speed instead of 1300, where as my Macbook Pro early 2015 can do 1300Mb/s with its 512GB ssd. Is it because the model I bought for the iMac is an older SSD? Or is it because of the capacity? What would happen if I put my Macbook Pro's 512 SSD in my iMac?