Project X Shafts Question | Golf Monthly

To be a pedant, PX flighted and PX do not play to the same flex. PX are about 0.5 stiffer than flighted.

To answer the OP, there is about half a flex, in old money, between the 6.0 and 6.5. Both are stiffer than TT DGS300, 6.0 by a bit, 6.5 by a fair bit, with 6.5 being in fact even a bit stiffer than X100.