I recently performed tests of 3 TDK medias (ALL manufactured by TDK, probably in Europe) on LiteOn 40x@48x and I got quite strange results...
TDK Ultra-reflex-x, certified: 24x, rec time: 2 min 40 sec
TDK D-view, certified: 24x, rec time: 2 min 49 sec
TDK D-view, certified: 48x, rec time: 2 min 59 sec
Burn quality is identical 99.89% or 100% on every media.
It looks that new media is "worse"/slower than old one...
Record mode: Mode1
Recorded amount of data: 693 MB