Just bought the Samsung T5 500GB SSD and ran some speed tests against the PS4 slim HDD. Not scientific by any means but got some some interesting results. See comment below. Btw
Samsung MU-PA1T0B T5 1TB External Portable Solid State Drive/SSD – Deep Black - Rebel Gaming
Samsung Portable SSD T5 Review: 64-Layer V-NAND Debuts in Retail
Samsung Portable SSD T5 Review (500GB/2TB) - The Industry Standard | The SSD Review