Al I'm familiar with the method that you are using and know it from another Luthier besides Robbie but it's not what I do. Wasn't the shaking out a top technique a Kent Everett thing?
Every piece of wood is potentially different in terms of stiffness, even if it's from the very same tree... So I deflection test and over time you build up a bit of a database of what worked for you and what may not have worked as well as one would wish...
But since this question is asked often on forums and has been asked on the OLF too the answer that I like to offer that comes from my own personal experience and also recognizes that we can't have the piece of wood that you are using in our hands or know it's qualities is this:
Where with spruce I might use .115" as a base thickness irregardless of any testing and .130 - .135 for say western red cedar with redwood I find that the sweet spot for thickness tends to be in-between spruce and WRC generically speaking.
Remember too that irregardless of top thickness a guitar top is a "system" where other important components including bracing and just how stiff one braces a top as well are every bit as important as top thickness.
By the way my numbers above are for a dread*ught shaped/sized instrument. I go thinner for OM's, L-OO's and thinner yet if I was building an even smaller bodied guitar.
These days for me the top thickness is not all that important in the greater context of the top's "system" including bracing, bridge plate, bridge, etc. I want the top to be thick enough to have some structure but not so thin as the braces will telegraph through over time although some of the finest guitars that I have ever played had braces telegraphing through the top and very slightly visible from the outside.
But after all of this long-winded stuff from me you should be fine at around .125 give or take .005".
Lastly when I started this Lutherie madness I wanted to be the kind of Luthier that has what I call a feel for the wood. You know the folks who can flex a top in their hands and have a pretty good idea where to go from there.
With Redwood it can be uber stiff with the grain but across the grain as we are flexing with no warning split right in your hands....
So be careful with your flexing across the grain and you should be fine.
Breaks my heart that people squander such a precious and irreplaceable resource. Next time grab it all and send it to me 
The only method I know that can be precisely communicated via text is deflection testing, but I'm a touchy feely type.