Just a quick update. The new public build (13A344) is slightly better than the GM build (13A340) released last week. The wake screen stutter is now gone so the only major stutter is the app switcher now. Again, it only happens every now and then. It'll probably be fixed in the next update since it apparently occurs across the newer iPhones as well.
Interesting. There's stutter on iOS 9, even though Apples only job was was to polish iOS 9 and make it run more fluid than iOS 8?