Hi-- I do some work with SCSI drives, so maybe I can help. One thing to tell you about the 160 interface (keeping it brief) is that one single drive will NOT use up all that 160 mb bandwidth, not even half that at 80. The drive just isn't capable of putting out that much continuous information.
If you want to save some $$$, I'd suggest getting an Adaptec 2940U2W, an 80 mbps card which will work fine with your hard drive-- the limiting factor will not be the adapter card, unless you're going to run RAID or something.
I'm currently using an IBM DDYS 18 gig 10K rpm drive on a system that has an embedded Adaptec U2W controlled on the motherboard-- that drive just rips through stuff!
One of my favorite haunts for SCSI stuff is <A HREF="http://www.hypermicro.com" target="_new">http://www.hypermicro.com</A>. Check their bargain basement for deals on some drives or adapter cards.
Hope this helps--