I don't think it's correct to base API comparisons using PC games.
many of these PC games are highly optimized usually for one renderer. For instance Quake based games run better with OpenGL, where as Unreal based games run better under D3D.
ePSXe is a great emulator, but it wasn't designed to take advantage of any specific renderer.
For instance Segu's D3D render is much faster than pete's OGL plugin. yet, pete's OGL plugin is faster than his D3D plugin. so It just comes down to software design and implementation.
But If I were to make a comparison between pete's plugins, on my new setup, I would say his OpenGl is faster and looks a little better than his D3D plugin. So that's the one I use.
ironically, D3D was faster on my old computer which had a TNT, I guess you can't win 'em all.