What are the objectives of running at these three different paces?
5% faster than 3 km pace - to improve leg speed and the ability to pick 'it up' in a race - specific endurance sessions would involve maximum distances of 1.5 km in a single repetition
3 KM RACE PACE - to improve VO2 max and resistance to fatigue and train the body to operate at the required 3 KM PACE - specific endurance sessions would involve maximum distances of 4 KM in a SINGLE REPETITION.
5% slower than 3 km race pace - to improve lactic threshold and teach you to function for longer periods - helps when there is a heat before the final - specific endurance sessions would involve maximum distances of 8 km in a single repetition.
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I think the fact that I found this "information" in the 3km training program tells you all you need to know.