Hartung,
Your research is very interesting... thanks for sharing. I don't think (and you seem to have proved this) high ring count is essential for heavy weight bows. High ring count wood is certainly more dense, and is more likely to make a heavier warbow, but not exclusively.
I've included a pic of some Canadian yew (taxus canadensus), which is very dense, at about 50 rpi. In one 1/4" section, the growth rings are so close, it's hard to determine numbers, even with magnification. This stave made a fantastic target bow, but was not long enough for a warbow.
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