Problem: Buffalo 8x internal writer stuck at 2x writing

[protonic]

Hello, I'm posting this because I need some help on my writing speed, which apparently is stuck at 2x. A month ago I purchased a Buffalo BR-H816FBS-BK, which can supposedly handle write onto BD-Rs up to 8x. Last week I purchased a 5-pack of Sony BD-Rs (labeled "Ver.1.2", if that info helps) which can handle writing speeds up to 4x, according to the label (while I would have preferred 8x discs, such were not available at the store I went). Now here is where my problem comes in: for some reason I can only burn up to 2x, which finishes one BD-R in about 45-50 minutes. I used two softwares: Cyberlink BD Solution's Power2Go (software bundled with the drive) and Nero 9's Nero Burning ROM. Both somehow determined that I can burn at most at 2x, as the 4x and 8x options didn't appear in the pulldown menus.

I would appreciate any advice on what I can/should do to burn at least at 4x speeds. OS is Windows XP. PC is a Core2 Duo with 4 GB RAM. Thanks a lot.