"...its been said that an asymmetrical design would be even more advantageous for a bow tillered for 3 under... but im having a hard time putting that together in my mind. it seems to me, that if my string hand is closer to the geographic center of the string, the more symmetrical the bow ought to be. thoughts?"
Eric, it's true that an asymmetrical design is better suited to the three under string hold than the symmetrical design... if keeping static balance (usually synonomous with geographic center) and dynamic balance in the closest possible proximity are valued. With three under, the asymmetrical design can put the static balance point, string hand fulcrum, and dynamic balance point all in practically the exact same spot. This may well produce the sweetest drawing and shooting bow possible.
In comparison, using a symmetrical design with a three under string hold would move the static balance point down to the center of the handle... which moves it away from the string hand fulcrum a little bit. Not a big deal, it just requires that a slight shift be made during the draw from static to dynamic balance points.
Coincidentally, shooting a symmetrical bow three under offsets the string hand fulcrum from the bow center the same distance as shooting an asymmetrical bow split fingered.
If I HAD to make a bow symmetrical, I would try to make it for a three under shooter... because symmetrical and split moves things too far apart for my liking.... but if I didn't HAVE to, I would elect to use asymmetrical bows for both three under and split holds.