"Incident meter directed straight at the sun: f/11 (no surprise!)"

Let this be Zone V.

"Spot meter reading off wet blacktop: f/64"

I get 5 stops here - so this would be Zone X. (Forget about all this 2.5 stops over 2.5 stops stuff.)

This should print as pure white and would qualify as a specular highlight, i.e. a highlight that has no detail.

Kirk - www.keyesphoto.com