Slope it 45+ degrees and add stone for a babbling brook effect

mjkat,
The answer to your question will depend on how you plumb the spa. Obviously, you want a maximum amount of water to flow over the spillway.
Are you using a single pump for pool/spa use? Separate jet pump? Separate spillway pump? Automatic controllers?
Each of these items will determine the plumbing method.
Ask your PB how it will be plumbed keeping in mind that you must draw all water from the pool and return it to the spa to get the effect you want. Some limitations will apply such as you will not be able to use the spa(in heating mode) and get maximum flow at the same time.
Good luck.

The photo in the link here is what I was thinking of doing. It is the 45 degrees suggested, but it will be a 1.25" travertine step-down (4 total steps, so the last step will be 4 or 5 inches). The stepdown is 7 feet wide. The Variable Speed pump that will run it will go up to 140 Gallons/Minute. Will this design give the babbling brook effect, or will it quieter than a shear descent from the spa?

Here is a link that might be useful:

mjkat,
That means you are expecting to get about 20gpm per foot of spillway. That's a lot of water and should provide plenty of noise for the effect you want. The gpm will most likely be a little less than the maximum you expect, but not enough to make a difference.
Generally the height of a water feature contributes to the noise factor as well as the amount of water.
With the VS pump you should be able to dial in what you want. Good luck.

Should I expect the noise to be greater with a single drop off, or will the step-down of the travertine enhance the sound? My concern is that some people have told me that the step-down (as seen in the picture of my last post) will make it quieter than a single drop off, while others have said the opposite.

Thanks!