A good CF card + PFS3 is a wicked combination for classics. 3.9 on my A1200 is booting in a few seconds, Mac filedisks are also lightning fast. Performance will be around the controller's maximum, the
SanDisk Extreme IV should cope even with the CSPPC/MKIII UW-SCSI. ;-)
Advantages: Cheap (in smaller sizes), silent, low temperature, low power consumption, low seek time, longevity, small physical size, performance blows away ancient SCSI/IDE drives typically found in older classics, easily removable for swapping files between computers
Disadvantages: 32MB largest size, still expensive in larger sizes, cost of CF card + adapter for SCSI applications