From Ars Technica:
You can’t get 12X speeds with all 8X DVD+R media. Only media from three manufacturers–Maxell, Ricoh, and Taiyo Yuden–have so far been approved for the faster rate. Taiyo Yuden discs are sold under a variety of brand names as well as its own, so you may not always know if you’re buying them. The PX-712A is fast with other media types, but doesn’t break any records. It can write to DVD-R at 8X, DVD+RW and -RW at 4X, CD-R at 48X, and CD-RW at 24X. It can read DVD-ROMs at up to 16X and CDs at up to 48X.