@jimmyz: actually i think they are pretty equal. I see only the 8->6 connector change and the field of resistors on the center/left. Both changed might actually be related.
@robal: thanks! I added the PowerTune differences. I already read the article but forgot about the PT
Edit: okay, I made out some more PCB differences, you as you pointed out:
- the silver/blue caps are "E063..." for 6950 and "E059..." for 6970
- the large silverwhite block at the bottom left is "25CH10 X7" for the 6950 and "36CH10 A" for the 6970 (production date is in front, so these might either be different fabrication lines or actually different chips)