Both rawhide and snakeskin will negatively affect the performance of the bow, if you take arrow speed into account. Both these materials don't add drawweight or reflex to a bow. However, they do add mass to the limbs, which ultimately is a bad thing performance wise. If bow performance is all you're after, you should leave the rawhide and snakeskin out of the equation.
On the other hand, rawhide makes a bow more durable, protects the back from dings and prevents small splinters from lifting. These can be really crucial factors that determine a functional bow, although these factors do not add to the performance of the bow.
A 60" hickory board should be able to make 27" drawlength, but 28" will be pushing it without a backing. How wide can you go? What's the drawweight you're aiming for?