I have used both fur and rubber, seem to work about the same for me.
I have TWO sets on my string, like wahya said i start with a catwhisker that is full length and then cut it in half, I use 1 set at the 1/3 and another set at the 1/4 mark and trim the two sets closest to the limb tips a little so that they are shorter.
My brace height that I have settled on on this particular bow is 7" the bow is 66" 54#@28". Shootting arrows a little over 620 grains.