I have a really aggressive overclock on my pi that gets most PSP games running nearly perfectly. I do have a cheap sd card though, I do see some sub-second pauses in quite a few games, but they’re still very much playable. I’ve tested an absolute ton of titles and have found over 100 games that work well. My psp games are on an HDD.
Here’s what I’m using, these are guaranteed to void your warranty, don’t blame me if you blow up your pi with these: