When I was in 17:30ish shape my long runs were 11ish miles at 8:00-8:30. My coach told me to go 90 minutes easy, so I jogged and figured out the average later.
This track season I've run 800/1500/mile. I would guess I'm in 15:30ish shape based on workouts and long runs. I don't jog long runs anymore. Depending on the the time of year/season I go 9-13 miles. Most long runs have an average between 6:20-6:40. Often with the last 4-6 miles faster than 6:15, last couple miles under 6:00. Every once in a while I'll average 6:00 or so, with the last 5-6 miles around 5:40. Very rarely do I average 6:50+. Our training week is set up well to allow fast, or fast finish, long runs.
Slow long runs may have a place in training for longer distances, but the 5k isn't that far. Strength and aerobic ability is crucial for 5k success, but so is speed and efficiency. I believe faster ling runs are simply more beneficial, as long as you allow enough rest and recovery. I do one hard workout mid week, an easier workout or race on Friday or Saturday, my long run the following day and then a day off. I have been able to stay healthy with this cycle and continue to improve.