Growiso doesn't work properly with LG GSA4163B burner and DVD+RW 8x discs. Burning speed is about 4x (even when burner speeds up switching from 4x zone to 8x - it's a ZCLV burner), it's well visible with K3b. There's no problem with all other types of media, including DVD-R 8X. It's certainly growiso problem because cdrecord.prodvd writes those disks at nominal 8x speed.
Tomasz
