My Adaptec 2100S does just fine at a 83Mhz FSB. I think that runs the PCI bus at 41Mhz. However, it actually CHANGES THE PCI LATENCY all by itself if I have it set lower than 64. I have an ASUS P3B-F
Try removing one of your sticks of RAM. You should have a 350W power supply to feed all that HW. PM me and I'll tell you how to get a better SCSI card for less than what you paid for yours.