First I would like to point out message by chipdip (sorry if
this irritates you)
With SCSI they don't called master and slave. Instead they
have SCSI id (they usually call LUN, logic unit in short I think)
ranging from 0 to 7. In case of PCs I think they can only be
booted from lun0 (without any particular 'boot manager').
Even you have 'ghost' your present system to the SCSI, you
will have to manipulate the bois so it boots from the SCSI
device instead of the CD-ROM or the IDE drives and I think
you probably know how to do it.
Not to discourage you, I don't think it can boost performance
too much if you are using for window (98,2000/client). It will
do some good if used in server application. But if you are
financially OK, no harm buying SCSI. (Tell me if I am wrong
about the last paragraph)