I used to use Rotella 5-40 in my suzuki and Jetta TDI. A shop that specialized in VW TDI repair noticed a a growing number of TDI's coming in with bad turbos. They had two things in common:
1) Shaft had bluing
2) Owners all used the reformulated Rotella 5-40 (which has less zddp)
I did an oil change with new rotella and clutch was grabby, shifting was notchy, switched to Maxima, all was better.
As for expensive oil oil, yeah, it is easy to spend $11 a qt, but I went to an oil wholeseller who also sells to the public and I get Redline bike oil, 10-40 for under $8 a qt.
It is a fact that rotella will shear down to a 30w oil, that is the VI stuff being broken down. It is also a fact that Kawa recommends a warm viscosity of at least 40w. However, in all honesty, I have yet to see an oil analysis of rotella (sheared down to a 5-30) showing elevated wear metals. In fact, you could probably run a high quality 5-30w synthetic with no ill effects. I saw a oil analysis of a ZX 14 where, after 1800 miles, the Rotella sheered to a 30w. Yet, metal levels (wear) were still in the acceptable range-go figure.
I think the most common reason for using Rotella is to save $ and people who do use it will often add that they change it often, maybe every 3500. I change my oil every 7000 miles or once a year, so that probably brings the end cost down to closer what it would cost if I used Rotella with changes every 3500 miles (I forget how much that stuff costs).
