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
PlayStation 5: the best external SSD upgrade options tested | Eurogamer.net
Amazon.com: SAMSUNG 980 PRO SSD with Heatsink 2TB PCIe Gen 4 NVMe M.2 Internal Solid State Drive + 2mo Adobe CC Photography, Heat Control, Max Speed, PS5 Compatible (MZ-V8P2T0CW) : Electronics
SAMSUNG 500GB 2.5" PS4 SATA HDD ST500LM012 HN-M500MBB/SP4 | eBay
PS4 Pro - Speedcheck: Samsung internal SSD 870 EVO vs. internal HDD (RDR2) - YouTube
PS4 Hard Drive Upgrade - SSD HDD and Hybrid – Billy's Toybox - W. Keyes
How To Upgrade The PS4 With A SSD For Original, Slim, Or Pro - YouTube
Amazon.com: SAMSUNG 990 PRO w/Heatsink SSD 4TB, PCIe Gen4 M.2 2280 Internal Solid State Hard Drive, Seq. Read Speeds Up to 7,450MB/s for High End Computing, Workstations, Compatible w/Playstation 5, MZ-V9P4T0CW :
Buy 1TB PS4 SSD (Solid State Drive by Samsung) Upgrade Kit - Compatible with Playstation 4, PS4 Slim, and PS4 Pro Online at desertcartEcuador
How To Upgrade Your PS4 Slim With a 1Tb SSD! - YouTube
Replace your PS4 Phat Hard Drive with an SSD - Easy Install - YouTube