It's not about speed. In equally well made strings, there's little difference in performance between dacron and any of the "FF" type materials.
The difference is: durability, consistency, stability.
I agree the average shot on a whitetail is probably 12-15 yds. Pretty sure my average is less than that. That boils down to how many shots a year...one, two, ten?
Now, what does it take to get that one, two, ten shots? How many practice shots? How long did you sit there (in the South it's still HOT when the whitetail season opens...dacron can stretch like crazy in the heat). What kind of crap did you walk through to get to your spot?
If it were just about one, or two, or even ten shots a year and nothing else had to be taken into consideration, I don't think there would be much to think about.
However, when you are practicing thousands of shots throughout the year; when you may be sitting for hours and hours before you get that one shot; when you may be wading through briars or climbing rocks or whatever to get to your spot...that's when the difference in durability, stability, and consistency...not to mention the huge difference in can make in how comfortable the shot it...makes a ton of difference.
No slight towards anyone or any bow, but I personally won't even consider buying a new bow that's not warrantied for whatever string I want to put on it, anymore than I'd buy a bow that required me to shoot a particular type of arrow, or a particular type of broadhead, or a particular type of glove, etc. But, that's just me.
Again, performance differences are at the absolute bottom of my list of benefits when it comes to strings. In a well made string, there's normally not enough difference to make a difference. There are lots of other things that do add up to a big difference.