Hi,
Funny you should mention oil analysis:

http://hiwaay.net/~bzwilson/prius/pri_toil.html
http://hiwaay.net/~bzwilson/prius/pri_T_cold.html

I've been sending transaxle oil samples for analysis and it looks live the viscosity, the primary oil characteristic, changes pretty dang quickly. Some of the additive levels can help but ordinary oil tests don't do a very good job of oil identification.

The reason I bring this up is good engineering is based upon a combination of physics, chemistry, math and measurements. There is nothing wrong with making a reasonable change when it is supported by testing. So when I switch to 0W-20, I'll also have not only the virgin oil tested but I'll also have a plan to take intermediate samples and test them. If there is evidence of a problem, I'll switch back and test. This is how engineering works.

Now I know folks who only 'follow the book' and I wish them well. I am amused that if you cross a border, Canada, Alaska or Japan, you'll find a new set of memos. But fortunately, that works too.

Bob Wilson