The Isshin-Ryu Fist

Vertical Fist, c/o Isshindo.blogspot.com

At one of our seminars recently my training partner and I were criticized for using the vertical fist with the thumb pressing on the top of the fist rather than wrapping around the fingers on the side of the fist.
I explained that I had seen the position used in other arts and over time had found I can speed hit much faster with this position. I feel this is partly because it is a more relaxed position. I no longer use the horizontal fist at all, anyway. I also feel that if I wrap my thumb (which I still do for really heavy hitting) around the fingers on the side of the fist, It tenses my fist ever so slightly. This tenses my arm, which tenses my shoulder, etc. I believe this heavier fist position makes for much slower striking.
Here is what Wikipedia says about this fist position:
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Beginning at the fist and moving up the arm: The fist is made by holding the hand open and then slowly curling the fingers from the most distal knuckle until a fist tight enough to completely hide the fingernails is made. Then the thumb is pressed down on the second knuckle of the index finger. Styles which practice a twisting punch frequently wrap their thumb down over the fingers, which begins the arm torque they use for their punch and this is precisely how Shimabuku taught it when he taught a twisting punch. Since Isshin-ryu punches straight ahead, the vertical thumb position allows for cleaner alignment of the wrist and arm bones.(A still picture of Master Shimabuku posed with his students shows the thumb not standing straight up, but rather laid over, touching the "web" of the hand. This position supports and protects the thumb, while maintaining the advantage mentioned above.) This position of the thumb also allows for it to be used as a specialty weapon for precision striking, or Atemi, at delicate and vulnerable targets such as the temple or other nerve shots.

The fist is held straight, lining up the bones behind the first two knuckles to distribute the impact to both the radius and ulna. The arm is relaxed, with the elbow and shoulder both tending down toward the ground.

The Isshin-ryu vertical punch appears to owe as much to the vertical punch practiced by the older Chinese form of Hsing-I as it does to its direct lineage in Okinawa-te. It is also believed that Shimabuku used the vertical punch in an attempt to distinguish his style from other styles prevalent at the time. While this view is not widely held, it is nevertheless one theory that has been proposed that has merit. The body structures used in the strike are especially strong at close range and toward the center of the body, providing a different set of optimal striking distances and postures from the more common twist punch practiced by other styles.
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(D.R.) So the debate begins; Am I full of crap or what? I really feel good using this fist position for certain punches. I can be much faster, more accurate for pressure point hitting and more controled. I can lay a series of hits right on the surface of the skin of a training partners face with absolute control. I also can hit boxing hand targets with no discomfort to the hand. Works for me.
I'd like to see what other folks think, and will extend the discussion to the new forum at "The Convocation Of Combat Arts".