I actually have both Dacron and FF stings from an old bow I no longer have so I can try both. How much difference is there in performance between the two?

Don't forget to use a heavy arrow, better for the bow.  Personally I don't think the difference will be worth it, but it's up to you.
Good luck..  

Differance well be 4 to 6 fps. And more noise with the ff string. I've got a Bighorn with tips that look like yours and its not rated for ff string.

I would use Dacron and not take the chance

I just strung mine up with Dacron, it actually feels better. At 60#, and I'm pulling 57, a few fps is nothing, however I gained a whole lot in noise reduction and life of my bow. Replacement limbs for these bows aren't as easy to come by as they were say 5-10 yrs ago.

I have several bighorns of that era,stick with the B-50 they will shoot much more quietly than with FF.I had the bomb proof tips installed on 2 sets of limbs and both sets did not hold up.I had them fixed and switched to B-50 and they are still going strong.

Don't get hung up on the speed gain it will be mimamal anyway maybe 5 fps.They shoot a heavy arrow with authority even with dacron.