Rob,
When the number of strands in the string are equal, a flemish has at least twice as many strands in the loops and is therefore stronger than an endless string.
Even if no "padding" was added in a flemish a 10 strand string would have 20 strands in the loops while an endless string would only have 10 strands in the loops.
I have ran chain through cast iron weights and attached the weights to a string by using "S" hooks. Doing "weight drop" tests to simulate the shooting an extremely heavy bow, I found that the flemish string held up better. Endless strings almost always break in the loops where the hooks attach to the loop and broke before the flemish strings.
I did this about 10 years ago and I don't remember at what point the strings failed, but if you want to know the particulars, I am willing to repeat the tests and report the exact findings. I don't remember what material I did this with either. I don't think there would be much difference in dacron strings since one doesn't typically pad the loops on a dacron string, but I would still favor the flemish just because of the higher loop count in the loops. I suspect I used dynaflight97 in my tests since it is my favorite material, and if that is so I suspect my flemish loops had more than double the loop count since I pad loops and would have most likely tested the products in the manner that I would use them. If that was the case, then admittedly my flemish strings had MORE THAN double the string count in the loops due to the loops being padded, but I don't believe that is cheating because that is also how I make them for bows as well. What I do remember is the flemish held up better and that part stuck in my mind.
When I make a flemish dynaflight of 9 or 12 strands, the loops have splices added to them to bring up the loop count to 30 strands. A flemish 30 strand loops is CERTAINLY stronger than a 9 or 12 strand endless.
Again, I am talking about when two strings are made properly.
Again, the biggest problem with flemish is finding someone that knows how to make them properly by
1. counter-twisting the individual bundles after
2. adding loop padding, but before
3. flemishing the groups together so one ends up with
4. a round finished product that doesn't look like 2 or 3 ropes wrapped around one another.
I of course do this in every string I make, and I believe Chad (LBR) does it properly as well as we have met and discussed string making, but far too many string makers do NOT do this properly.