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
Portable SSD T5 | Samsung UK
Samsung 500GB T5 Series USB 3.1 Type-C External Portable SSD (MU-PA500B/EU) | BT Shop
Samsung Portable SSD T5 Review (500GB/2TB) - The Industry Standard | The SSD Review
Product | Samsung T5 MU-PA1T0 - SSD - 1 TB - USB 3.1 Gen 2
Portable SSD T5 | Samsung UK
Samsung T5 500 GB USB 3.1 Gen 2 (10 Gbps, Type-C) External Solid State Drive (Portable SSD) Alluring Blue (MU-PA500B) : Amazon.co.uk: Computers & Accessories