Why is there debate? Just trust the manufacturers' recommendations.
It was a shock when our family went from domestic (5000km) to German (15000km). But hey, if the manual and the dealer both say it's good enough.. good enough for me. Their engineers aren't stupid. Neither are their lawyers.
Maybe I'm just being new school, but with all the improvements in oil technology over the years, that 5000km limit is simply obsolete if you're going synthetic imo. Sure you can change it more often if you want; companies like Quaker and Mobil and Castrol thank you for your business.
Same deal with the weights. Just go with whatever the service bulletins/manuals suggest. Why mess with it?