The Sony DW-U10A to DRU500A and 4x firmware hack roundup I found is a nice summary of firmware hackers making their DVD a real DRU500A an capable of buring PRINCO 4x media at 4x speed.

succesful 4x WriteTested media:

Princo 1-4x DVD-R type: Whitetop noname 100 spindel
Princo 1-4x DVD-R type: R4.7 4x/1x
Philips 1-4x DVD+R type: DVDR1S04/200

Read more at The Sony DW-U10A to DRU500A and 4x speed roundup