well i used those:
linuzappz Iso CD/DVD 0.7.0
CDVDnull driver 0.6.0
those work normal (i think at least)
on the other hand P.E.Op.S. CDVD (CDDA mod) 1.3.0
didnt worked it says that plugin cannot be used.
uhm, use latest GSdx with 512x512 internal resolution as graphics plugin use ZeroSPU2 for audio plugin enable MTGS/DC in cpu config options if you have a dual-core cpu or better and last try using frame/vu skip in cpu config options as well. Tell us ur system specs for more specific info.