Tempo runs are one of my faves. During marathon buildup I’ve gotten up to 7 miles of tempo plus warm up and cool down, those can be tough but rewarding. They definitely help with speed!
I haven't done many before, but they are definitely growing on me. Easier to convince myself to do than intervals. I plan to increase the length as I ramp up my mileage, probably not all the way to 7 miles though!