The scsi speed depends whether you're talking about the speed shown by a benchmarking tool such as scsispeed, or whether you're talking about actual transfer speed of files.
In the first instance you will probably get benchmark speeds of around 8.5 - 9 MB/s (with sufficiently high buffer settings) independent of the filesystem used.
If you try - for example - dragging a 100mb file into your ram disk, then copying/moving that to a device on your scsi chain the speed will probably be around 1-2 MB/s - maybe 3MB/s at a push.
Theoretical vs actual speeds. The scsi bus may be capable of transferring at that speed, however add the inefficiencies of filesystem, transfer protocols, disk access speeds, etc and the actual transfer speed is a lot lower than the nice high figures shown by scsispeed. At least that's my experience.
However, nearly 100% cpu free whilst doing large transfers and still significantly faster than the on-board-PI/O IDE port, and up to 7 devices (including scanners, etc). SCSI is still well worth the investment IMHO. Just don't expect 8MB/s read/write speeds on your hard disks :-).
Might be worth checking that you have sufficient buffers assigned, and that your Mask settings aren't restricting you to chipram or 24-bit ram -
this topic may be useful insight into the settings.
