How can I twist RetroArch configuration for better performance?

I don’t know how it is now, but I played PSX games without problems and with good FPS (enough for me, don’t know exactly how many) by running PCSX reARMed natively, not through the RetroArch core. The core was very slow, but running the standalone work fine!

Take a look at this post: PCSX ReARMed for GameShell

You can make shortcuts as well on the “Home Screen” to run games on the standalone emulator.