ORIGINAL: 5 shot
To figure the cutting surface I take the cutting diameter and divide it by two, then multiply the number of blades by that figure. I then add in any cut on contact tips or blades that are not full size. The blade thickness issue generaly comes out in the testing. thicker blades tend to hold up better and not break in the plywood, tire and drum.
For arguments sake:
Would it be more meaningful to include the length of the blade's cutting surface (i.e. blade's length) into the calculation of the total cutting surface? This to me would be logical since this has an effect on penetration due to friction of a longer blade versus a shorter blade.
A steeply angled short blade such as the nitron or the slick trick might have the same cutting diameter as say a less steep thunderhead, but the thunderhead has a longer blade and therefore technically a greater "cutting surface." One would theorize, if ferrule diameter and weight were the same for each, that a thunderhead would penetrate less and we could perhaps prove it mathematically.
Mabe have two factors: Cutting surface and Cutting area? Or something like that?
Great stuff btw 5-shot!