Older Fextras were known to be faster and stiffer. The Fextras I've bought off Aliexpress have all been in the lower to mid OFF- range (1313-1333 hz). So it's not fast at all if you don't use fast/bouncy rubbers.
I've used Yinhe Mercury 2, Loki Rxton 5, 729 Battle 2 Pro, and Loki Rxton 1 Plus...