I'm looking to upgrade my Early 2015 MBP Retina to a 256GB or 512GB also. I see some original Apple/Samsung SSDs for sale on eBay but they advertise them as compatible with 2013 - 2015 models. I've read that the Late 2013 and Early 2014 models came with PCIe 2.0 x2 5.0 GT/s (8 Gbit/s) and the Early 2015 model came with PCIe 3.0 x4 8.0 GT/s (25.6 Gbit/s). I would not think that they will be compatible with each other. I would like to find one that will run the fastest with PCIe 3.0 x4 8.0 GT/s (25.6 Gbit/s) my system supports. Does anyone know the model number of the OEM 256GB or 512GB that would have originally came from Apple so I can look for it?