Update: More information about this topic has been posted in this thread:
CD-DVD Speed Disc Quality (PI/PIF) Test (link is to the start of the relevant discussion)
It's actually possible to scan at 1 ECC at the 4x (CAV) scanning speed if you press the "Advanced" button before scanning. The 8/1 ECC scanning interval in the options window is ignored however - it's the pressing of the "Advanced" button that changes the drive to scan at 1 ECC but only at 4x CAV.
The mystery is explained by ErikDeppe here in that thread.