They have a page for benchmarks. For both read and write, RaSCSI is faster than original hard disk Apple Macintosh (intended user) shipped with.

There are benchmark results using a X68000. Random i/o is comparatively good (as one would expect), sequential large reads is just about 1MB/s. Still much faster than floppy disks and not too far of the theoretical maximum (5MB/s for SCSI-1).