Looks like you are getting the best results with CG5G. The recalibration feature in that firmware should help your problem the best. Are you following good burning procedures and not surfing/multitasking during the rip or the burn. Is your HDD defragged and have ample free space for the image? I assume so, but just thought i would mention it.
You said you are getting good results from other stuff, its just these R02s and usually at the end. I have found that moving around the spindle a lot can cause movement and friction and damage between the discs themselves, particularly at the edge where they come into contact when moved. So find a spot for them and leave them there, or move them carefully.
Saving my best suggestion for last...use the bad-ended discs for short movies:)...sounds funny, but it works.