Fastest bow (not chrono tested but clearly shot fastest) I've made was backed, but i bet it's because of shape, not the backing. Comparing to a similar backed bow I made some years ago (both 55#, both 72" bows, 2" wide at handle to mid limb, 6" stiff skinny tips, 6" stiff handle, hickory backed, trapped) the new one shoots noticeably faster. The new one holds a little over 1" just unstrung reflex, the other about 1 1/4" just unbraced set.
I'll agree with mikekeswick, the best bow is the one you have the most fun with.