OK, back from the trenches [OK, LA freeway] reporting back on the results of actually calculating spark timing, using the superhonda formula. In short: it's a crock of poo.
The problem is he's got the single most crucial factor trivially set to a flame-speed constant times the combustion chamber *height* around TDC. It's completely and utterly wrong.
The mechanical calcs are probably OK for a first approximation; it more or less assumes that the chamber volume is constant during the flame time. (we know this is not true).
The gist of it is this: for all speeds the charge burn time is assumed to be constant, and very brief -- flame speed multiplied by the combustion chamber *height*. That's nonsense; the chamber is only .030 - .050 whatever high, but it's inches in diameter, duh, the flame spreads *sideways* and all-ways. Plus it's dynamic -- don't need no theory to notice spark lead isn't simply proportional to RPM.
According to his calcs -- with anything in his recommended flame speed range -- my spark lead should be between 0 and 10 degrees. I know from careful experimentation that it wants more or less 26@2500 WOT, etc.
So -- assuming that 15 degrees ATDC is where max pressure wants to be (close enough for this purpose) -- and going from OBSERVED REALITY, I back-calculate that my effective charge burn time is about 13 milliseconds at 500 rpm (10 degrees lead), and 8.8 mS at 2500 rpm (26 degrees lead) at WOT. That's more than 20 times off his simplistic calculation.
OK my mixture varies with air speed (carb) where FI is probably more linear. Still, his calcs are useless. The point is, it's far too complicated to have a one-size-fit-all formula.
The answer is what we always knew: start with something (like stock) and tune til correct.
