Mr Big: Actually, a lot of newer hdd:s might also take serious damage if you run them at 40+ MHz for a long time. Furthermore, many sound cards sound like crap if you get that high. Also, many cheap network adapters die already at 38 MHz. So I wouldn't really go above 38-40 MHz on the PCI unless I really had to...
Edit: that looked very "mean" when I said it like that... Sorry, but the hdd:s really can take a lot of damage, especially in DMA. But you're right that older hdd:s are more sensitive, of course. 🙂