Having just installed a new CD-RW drive, I tried to burn an audio CD at 16x on some MMore disks which are about 2 years old. It failed, but worked at 4x. Should you really take notice of the speeds quoted on disks?
It think it is fairly wise to pay attention to the speed certificates, even though higher burn speeds are often possible and work well. If I remeber correctly older MMore's are CMC Magnetics made so you might be having quite a low quality discs there.
