Twenty strands of BCY-X is what I use on my indoor target bow, and it's pretty much identical to 12 strands of Dyna97. Personally, I've never seen any reason to go thinner than that.
Same here, although I have dropped to 18 strands on some lighter draw weights.
For anyone who might not know, Jason is a World Champion archer, a very accomplished hunter, a string maker, and has written articles for archery magazines...amongst other accomplishments. His credentials are matched by very few.
To get to the question at hand, I wouldn't go with any less than 14 strands for 55#. I won't be going that low on my own bows. 18-20 has worked very well for me.
It's not wise to base these decisions on a best case scenario. X is very strong, and very durable, but something could go wrong.
Ask yourself a simple question: why?
You might pick up a couple of fps, or you might not. You might change the noise level, or you might not. Neither is going to be changed enough to affect hunting or target shooting. What you definitely will do is affect the durability and strength of the string.
Speaking for myself, I don't shoot traditional bows because I worry about a couple fps, or because I want to take the easiest route. I know if I do my part with tuning and choose the correct arrow, I can get my bow VERY quiet. I know that by doing something as simple as working on my release I can pick up as much as 10 fps or more without changing a thing!
Lastly, I am fortunate to know some pretty dang good archers. None of the best I know use tiny strings.
I'm not saying this to aggravate or insult. It's just simple facts as I see them. If anything, it would be to my benefit to advocate low strand count strings. I won't, because in 20 or so years and thousands of strings I can't find any tangible evidence that they are better, and they do have shortcomings.
My opinion. Take it for what it's worth.
Chad