Thanks for your feedback.
I spent this afternoon to find out more about the performance of external drives. Finally, I came across a test in German computer magazine c't 8/2005 where the following results were reported:
Though in German, you can get an idea of the performance of the tested cases if you look at the three lines following 'Messungen' which give read transfer rate, write transfer rate, and max. burning speed that can be reached under USB resp. FireWire. Best results shows Mapower MAP-KC51C1 due to the used chipsets (Genesys GL811E-04 for USB, Oxford911Plus for 1394a). Perhaps easier to read is the following graphical summary
which clearly shows Oxford911Plus to be the most performing chipset. Surprisingly, it even surpasses all USB chipsets' read and write performance (except Genesis Logic GL811E-02 which equals in write speed but is far inferior on reads). c't summarizes that MAP-KC51C1 can burn at 12x with USB and 16x with FireWire.
The superior performance of Oxford911Plus is backuped by the following very detailed article:
I don't know how all these results relate to the lacking UDMA4 support of DW165x. On the other hand, I agree that 16x isn't really an issue: I prefer quality burns to highspeed burns, and at least for the moment most experts recommend to burn 16x media at 12x.
Unfortunately, the German Mapower site recommends not to use BenQ drives with MAP-KC51C1 on Oxford bridges. I've sent a email and asked for details. I'll keep you informed.
If there are really incompatibilities with DW165x, which alternatives should I look for: LiteOn, Plextor, NEC? Any recommendations?