50Hz runs pretty much on any flatscreen TV, US, EU or anywhere else. Yes, modern gaming systems don't use "PAL vs NTSC" frequency anymore, they are usually 1080p 60hz.
The issue with PAL PSX games is that the gameplay runs slower than NTSX and for people that grew up in the PAL area, that's not an issue. In fact, for europeans the games "feel" like they did back then when we played them - arguably not really a bad thing.
For NTSC regions, that's different, though. They were used to the games running in 60hz, resulting in faster gameplay.
It's something I notice every time when running the US version of games like Super Mario Bros. 3 on any NES emulator (including the NES classic) - it runs faster, the music sounds different, etc. It just doesn't feel like what I used to play as a kid. And Sony caused the same issue for americans now - for this audience, the PAL games feel too slow and from what I could gather this affects not only a few games of the lineup but quite a considerable portion.
What would be nice to know: What mode does the PS Classic run at when playing these PAL games? Does it switch to 1080p 50Hz or does it run at 1080p 60Hz with interpolated frames? That would most likely look horrible.