<< I run a 158 MHz FSB now, 39.5 MHz PCI. My IBM 60GXP has never complained. I was wondering if the WD drive is as tolerant. >>
Like I said, it's potentially a disaster waiting to happen. It might work fine, but then again it might not, and in 2 months you may end up kicking yourself (unless you have adequate backups). Only time will tell and YMMV.
I have found my IBM drives more tolerant than others, but 39.5 is really pushing it. (I haven't tested any recent WD drive though.)