I went from a WB with the brown/black bristles to a NAP 2000RG drop-away and gained 8 fps. I was using helical feathers on my arrows. I had good accuracy with the WB but much better with a drop-away. I mainly changed due to the wear I was getting with my feathers.

go to my website www.broadheadtests.com and read my WB review. It should help answer some of your questions.

Do you really have to break them in?

I once trimed a biscuit and added three notches in the bristles, for the vanes to pass through. This configuration actually gained 2 fps over a conventional prong rest. Personally, I wouldn't worry about a couple fps in either direction. It's virtually meaningless.

I know that with the original black bristle variety it helped reduce fletching damage considerably.

Exactly. The only situation where it would matter in my opinino is if you are borderline with KE levels and are trying to tweek out every last bit of speed without sacrificing arrow weight or overall shootability.

In my experience it has been about 5 fps.

The old style biscuit probably averaged 1% speed loss compared to a dropaway rest. There are factors that would effect this number. Using three inch straight fletch feathers the speed loss would be hard to measure. The state of tune of the bow will also have an effect on what will be lost. I usually tie in a nockpoint with a piece of bowstring and the difference in speed between using a brass nockpoint and one made of bowstring material more than compensates for any loss from the biscuit. The new B-2 biscuit shows no speed loss compared to a prong style rest. Good luck hunting!