If the physical weight of the shafts is the same, they'll shoot close enough that you won't know the difference. On average, Sitka spruce runs a little lighter than POC, and Doug Fir, a little heavier. Hardwoods, of course, are much heavier. If you change wood species, be sure to order them at the same physical weight, if possible, as well as the same spine weight you're currently shooting. If you can't get the same physical weight, you might have to go up (or down) a little in spine, but probably not more than 5# static spine.