@ Robert
CyberSCSI is a module that attaches to a Cyberstorm accelerator (you can't buy a CyberSCSI module and use it by itself). If you want to go that route, you will have to get a Cyberstorm first. And if you're going to get a Cyberstorm, you can do yourself a favour by trying to get a MK3 because it has an onboard Ultra-wide SCSI controller. You'll battle to find a Cyberstorm MK3 for sale though.
But the alternative is worse: trying to get a MK2 (which has no onboard SCSI) and then trying to find the CyberSCSI module for it. And you might find that a MK2 and a CyberSCSI module cannot be overclocked (that is how it is with mine). And the CyberSCSI is not Ultra-wide, it is Fast SCSI which is slower. So if I were you I would ask myself a little question: "How much am I willing to spend on an accelerator for my A4000?"
If you don't have a cash problem, then go for an accelerator that has an onboard SCSI (don't try to get the two components separately).
But if cash is tight, then you should get a Zorro-based SCSI controller like the Z3 Fastlane or the A4091.