Piper inner here! I found the excel endless loop dacron and flemish dacron the same fps but flemish stretches, not worth the hassle in my book, but others like them. The difference seems to vary from bow to bow, but would say about 15 fps is average. It's also 4 clicks on the V-zone at 20 yds. I'm using the excel on my phoenix and the fff on the emax. All shoot same arrow, 431 gr. W/ the endless loop dacron on Emax I was at 308 fps and 290 w/ Phoenix. Doesn't make sense, huh? w/ fff on Emax I'm at 328 fps. Got picks of the strings if you git confused, lol, happens here once in awhile, lol. Edited to add: I forgot to tell ya that on Excals, the fastest fps is gotten w/ string adjusted to about a 1/8-1/4" above lowest scribed line.[near riser] That doesn't matter to me, which may explain the above non typical variance w/ Emax and strings. I would have left it at 308 if I didn't have the Phoenix at 290, btw. dan