Wow! Herb_Master, very thorough research!
A few quick additions:
1. In the book China Oolong Tea (no English version yet, but the first half is very good about history) by Gong Zhi, the author mentioned that by Song Dynasty (around 10-13C), there was already gong fu tea drinking in Guangdong, but the tea was mostly from Fujian. At that time, people in Guangdong called their tea "Fujian tea". By Ming dynasty (14-16C), people in Guangdong still drink mostly "Fujian tea". Then in Ming Dynasty, Gongdong Feng Huang Shui Xian started to be produced in large amount to satisfy the market. The author cited historical poems and letters in which tea in Guangdong was called "Fujian tea".
2. Based on what I read, most scholars believe feng huang shui xian is from Fujian, but some believe it's from Feng Huang Mountain region and even Fujian shui xian was from Guangdong. In one article, the author cited Lu Yu's The Book of Tea (which is the oldest book recording tea drinking). The same article also mentioned that according to some record from Song Dynasty, tea from "Feng Mountain" was a royal tribute tea. The author interpret "Feng Mountain" tribute tea as "Feng Huang Mountain" shui xian. The above 2 lineage of evidence were also used by some other scholars to support that shui xian originated from feng huang, Guangdong.
3. By double checking the citation from the article I mentioned in "2", I found that in Lu Yu's book, tea from Shao Zhou, Guangdong, was mentioned. But Shao Zhou is not in Feng Huang region of Guangdong. So most likely the Guangdong tea mentioned in Lu Yu's book is not Shui Xian at all. Also the "Feng Mountain" mentioned in the book of Song dynasty is very likely to be another location in Guangdong, not far from Feng Huang, but not Feng Huang. So the evidence cited in "2" is not quite valid.
4. The author mentioned in "1" is from northern Fujian. The author mentioned in "2" is from northern Guangdong. To me where the tea originated doesn't matter at all. Fujian is a small province. Fenghuang, Guangdong is steps away from Fujian. It's not all impossible for the similar shui xian varieties to be naturally established simultaneously in both Fujian and Guangdong. But it seems that to local people where the tea originated and who was the real ancestor of the tea is a huge matter.

I remember there was a very old post dug up recently on this board about ancestor of some oolong or black tea. It was a long, long post with unclear language. But it seems the poster tried to say that tea originated from his hometown, cultivated by his ancestor, not elsewhere, not anybody else
5. Recording of tea history has not been formal during the past hundreds of or thousands of years in China. Drinking tea was simply a spare time hobby and not academic. Therefore writing about tea and studying tea history was not respected as some serious work. So historical record about his is not complete or systematic, and there are surely invalid sources and contradictions between records.