In the RC world, 150 watts/Lb is suggested for aggressive aerobatics, 200+ watts/Lb is suggested for 3D flying. More is more gooder, they say.
150-200 watt/LB is the general range that has been mentioned over the years as effective for stunt use. = 9.5 watt/oz to 12.5 watt/oz.
Tim's 175w/lb (11watts/oz) number is safe to use and given his EE background, it is probably a more informed recommendation than most can give, including any of my comments.
As an example, in a 53-54oz plane, I have used both the Cobra 2820/12 970kv (rated 590 watt) and the larger Cobra 2826/10 930kv (rated 660 watt). Same prop was used with both motors, a cut down 12x6 prop to 11". I swapped the motors back to back to evaluate nose weight changes rather than solve any performance needs. Performance and power seemed basically the equal between both as far as I could tell.
53oz @ 150watt/Lb = 496 watts required
53oz @ 175watt/Lb = 583 watts required
53oz @ 200watt/Lb = 662 watts required
In my ~64oz stunt ship, the BadAss 3515/580kv on 6s is rated for 1070 Watts. Using the 200watt/lb figure, my plane's requirement is still only 800 watts. The plane has excellent vertical and overhead performance. Cool running system. No complaints!