this is odd. i have a dvr-212d pioneer, a few months ago i burnt off a batch of dl at 4x with verbatims and memorex dl media w/o problems.
(sata burner on asus p5w dh deluxe mobo)
recently it kept failing power calibration on dl discs but sporadically worked with single layer so i felt it was dying (less than a year old)
bought a replacement dvr-212d but v1.24 fw seemingly won’t burn faster than 2.4x on supposedly 8x dvd+r dl 8x rated discs (philips) using nero 7.