TJ,
I think Chris is confusing their synthetic blend with Shell's new Rotella 5w40 synthetic. As you know the Rotella 5w40 is very new to the market.
With the new 5w40 I don't think you will need to dump as soon as dino oil, but oil analysis will let you know that for sure. I would assume you could run this 10,000-15,000 miles w/o any problems. If you do decide to run this oil make sure you have an oil analyis where they test TBN. This is a very important number when helping to determine how long to run the oil.
As far as comparing the Rotella 5w40 to Amsoil, keep in mind that it is not comparing apples to apples. The Rotella isn't in the same class of synthetics as the Amsoil.
-Ryan