At last I found this fascinating pdf file from Sony France detailing the real differences between their different tapes:

http://www.sony.co.uk/res/attachment/file/41/1167924780841.pdf

More info at:
http://www.sony.com/DigitalMaster

Thanks for posting this, Colin -- much appreciated,

Perhaps Im overly cynical, but it seems like its an exercise in marketing.

Perhaps Im overly cynical, but it seems like its an exercise in marketing.
Of course. It's their brochure, which is always marketing. But it's still useful information which I have been unable to find until now.

This page allows you to select detailed descriptions of all 3 categories of Sony's recordable media. If you poke around on the Web, you can find numerous "White Papers" that Sony and other manufacturers publish about these products and they may contain R & D data. To a video geek, this stuff is better than XXX-rated magazines, on a cold winter's night.

Once, about 15 years ago, I contacted the Sony Recordable Media Div., asking about the longevity tests they'd done on metal tape. A week later, I got a package from them by UPS, that had about 10 lbs. of white papers and product brochures. Far more information about particle sizes, shapes and orientation techniques than I could ever hope to absorb. Not likely you'd get such a response these days, with the Internet having taken over.

http://b2b.sony.com/Solutions/category/recordable-media