I can confirm that the BenQ DW1620 is very shaky when it comes to an overclocked PCI bus.
Even at a mere 5-10% Plus (and of course with timings adapted to the higher clockrate in the IDE drivers - Linux) it tends to hang up, though every other hardware ran fine - these include several different SCSI adapters (NCR, Sym Logic, Adaptec), IDE hdds (Samsung, IBM, WD) and DVD writers (LG, NEC, Plextor).
The shocking thing is, even if you "overclock" by a mere 1% (which is below the PCI bus allowed clock variation AFAIK) the BenQ occasionally gets unstable/hangs up, which makes me suspect a badly designed IDE interface.
My only conclusion is: If you want to overclock the FSB/PCI/IDE, dont buy a BenQ.
EDIT: Maybe its just luck whether one benq likes it or not...
PS: Person above has 10% overclocking and says it works. From my experiences, I can only say: It works ... mostly. But sometimes it causes my whole IDE bus to hang and such stuff. Obviously there is no guarantee all BenQs work.