Ok, this is interesting.
I've been running my PS4 with a Seagate Momentus XT 750GB 7200RPM SSHD since launch, and that's been working well. Recently bought a 1TB Samsung Evo SSD for my PC, but I thought I'd give it a spin in the PS4. It's been updated to the newest firmware, and verified to match the specs for read and write on my PC.
So I fire up The Last of Us Remastered on the Samsung SSD, and load into my game, which is in the prologue right at the beginning, with the daughter standing in the bedroom after getting a phone call.
44 seconds.
That's not very fast. So I put the Seagate SSHD back in and load the same save game.
33 seconds.
I've now tried this a few times, and it's depressingly reproducible. Other games like Knack loads a little bit faster, but TLOU:R just doesn't like the SSD. I've made sure that the PS4 isn't downloading anything in the background on the SSD, but the results stay the same.
Would anyone else with a similar SSD be able to test this? (Probably not, since this makes the SSD look bad

)
Might be worth keeping in mind before plunking down a huge sum on a SSD, at least if my findings are reproducible on other PS4 consoles.