you think that you only move on the same cable...no, you are shifting the data to the cpu into your CloneCD software and shuffle the data back into the same cable, this time as image data to the HD.
I doubt it has to do with the CDROM.
Try to just copy a CD to the HD with Explorer and check the time..
Which CPU and how much memory do you have? Which SCSI-adapter, which kind of SCSI HD, is it defragmented?
The advertised speeds are only possible under certain circumstances, temperature, RAM, so many factors...one more thing, does this happen with all CDs...or only with self-burnt ones? Sometimes CDs are unable to allow highspeed access.