Also, some skins have remarkable patterns towards the tail or the head. Rattlenakes and bulls for example have great striping towards the tail end but the bulls have a black pattern at the head which(in my opinion) isn't as striking. So although a big bull will easily do two limbs, I like two smaller buls to get the tail striping on both limbs. Here's some examples:
Tail stripes on this pair of rattlesnakes was incredible. Using two whole skins gave these stripes on both limbs.
This timber COULD be split, but I'd center it and use the outsides to adorn a quiver or knife sheath. When snakes get this big, its tough to use on arrows.
This bull shows the black scaling at the head and the striping at the tail. Although a phenominal skin in itself, On a longbow I think it looks better with both limbs having tail stripes.
Heres a shot of a limb with the black bull scaling from trhe head, still looks cool I must admit, I just really like those tail stripes.