Keep in mind that some brands tend to switch CD Factories for their CD-R media. Verbatim has always used the ones from Mitsubishi, which always worked well for PSX backups.
Have a look here to verify from which factory your 40x speed Verbatims are:
http://cdmediaworld.com/hardware/cdr...actories.shtml
http://www.megagames.com/psx/psx_cdr_media.shtml