Crank length, two different formulas

I’m not going to argue if cranks should be different lengths depending on how big or small you are, it’s obvious to me that someone taller should use a longer crank and the opposite if you’re short.  I’m beyond debating that point. But what I’m not clear about is who’s formula is most accurate. Keep in mind no formula is exact because I’m sure leg ratio, the type of riding you’re doing, your preferred cadence etc. all will effect these numbers a little bit.

Formula #1 by Lennard Zinn

multiplying your inseam (in millimeters) by 0.21 or 0.216 = length of crank in mm

http://www.zinncycles.com/cranks.php

Formula #2 by Kirby Palm

L(mm) = 5.48 x I(in)

http://www.polaris.net/palmk/Crankset.html

http://www.polaris.net/palmk/resume.html

I’m currently leaning towards Zinn’s formula and my tests I’ve done so far seem to prove it right, at least to me. Also keep in mind one of these formula’s was made by a bike builder, avid cyclist and former racer, where Palm well, I think he’s a smart guy, but I don’t know where he comes up with his numbers for his formula and I his about page does not paint the picture of someone who practices what they preach. I see Palm not having any history as an elite cyclist or bike builder and avid cyclist, but that of recreational cyclist that happens to be an engineer.

Let me know what you think?

Have you ever tried different length cranks, what was your experience?