On the few games I tried on it, they all ran full speed with no modifications made beyond default, or only minor custom config modifications. It runs a lot of games at least as well as many emulators that have been around for many more years than this one has. It runs well on AMD Ryzen processors as well, because that's what I got in my PC. If you can run Dolphin, or Cemu and get full speeds, then most games on RPCS3 will probably run full speed for you as well.
All these games ran great for me, with zero issues:
Demon's Souls
Tales of Xillia 1 & 2
Tales of Graces F
Dragon's Crown
Had to make custom configs for a couple of them, like Tales games have 60fps in battles, and 30fps outside of battles (on an actual PS3), and there is a setting and you can enable a setting in the custom config for this. If you get audio crackling (randomly), I had to set PPU threads to 1 instead of 2 in the custom config file. There isn't an option, you gotta open it with notepad and change it.
You can upscale the resolution to 4k for basically no performance hit on GPUs that aren't toaster tier. And I don't get any of the ghosting I typically get with some other emulators when I scale the resolution up to 4k. I can even stream it to my 4K TV, and play on the couch, and it looks great.