the clearances in the 5.4L '00 cobra R engine aren't different than regular production. ford factory fills and recommends mobil 1 15w50 for that car.
a friend who pounds his LS1 camaro in open track events uses mobil 1 15w50, since new, and the engine has made more power every time we've dynoed it.
it (or something similar) is probably a good idea in an engine that will see elevated oil temperatures. what's the standard viscosity test, 100 degrees C? why not show us what happens when it's 150 degrees?
of course, my point of view is always motorsports, so ymmv.
-michael