Most all bows are different. I've gotten as much as 11 fps gain in speed using 8125 over UltraCam---on one bow. Another bow I have I gained nothing. The biggest advantage you get from after market strings is not always speed, but stability. The strings creep a lot less so the bow doesn't change near as much, if at all, once it is set up and tuned.

Then there is the advantage of being able to use a peep without a tube aligner, as good strings don't twist during the draw. This might give you a gain of 8 fps or so all by itself. And make the bow more quiet, too.

Simmshunter, Gibblet here on this sight is the same guy as Bucknasty on Archery Talk. And his strings compare very well to the Winner's Choice on one of my bows---at half the cost. In fact, his end servings were even better.