I've only had it for an hour now. Apps load faster, MMS messages send faster, linked up to my Dodge Durango via Bluetooth in 2 seconds, where before it would take 15-30 or a need to turn off/on Bluetooth and try again. Even typing on my SwiftKey keyboard seems faster. Sometimes there was a delay.
Screen seems brighter and phone is warmer then usual, but that could be because of everything installing/updating post update.
Update:
Can't get the phone to be at a "resting" temperature, which normally for me was between 75-85°F. Anything above that and I knew someone was eating my battery in the background. It's staying in the 92-96°F since updating to Marshmallow.
Turned off WiFi calling, Voice over LTE, location, and even auto sync. Cleared cache from the bootloader menu already.
Got it down to 80°F by putting it in the freezer for 2 minutes, but it's back to 96° now.