http://psxdatacenter.com/ is worth checking out it has recommended settings for just about every game
when you use high end 3d graphics plugins there is no one setting that will work with everything some games will need tweaking up a bit to get working
e.g.
Graphics Plugin Pete's OpenGL Driver v2.9 ( internal X & Internal Y= Very High, Stretching mode: Stretch to full window size, render Mode: 2 (Use framebuffer object) text filt = 2 FPS limit= 63, Compatibility=2,3,2; Shader effects= 1 (Fullscreen smoothin))
Audio Plugin ePSXe SPU Core
CD-ROM Plugin Sapu Cdrom plugin v.1.3