I have some Teac 6x and 8x external SCSI drives and had no issues burning CDs with my IIfx. I hink I used Toast 3.5x? You are limited by the external SCSI controller wich on most 68K macs is slower then the one the internal devices use. Still I don't see why you can't get 1.2MB+/sec out of the external ports which is good enough to burn 8x.

http://support.apple.com/kb/TA29470?viewlocale=en_US <== shows max data rate for various 68K machines.

So a compact might be stuck at 6X burning.