Isn't 60 % fat burning territory, aerobic training can go up to about 85 % of max heart rate, above that its seen as anerobic training (although both things occur in tandem truth be told).
If the goal is to get fitter and faster then don't be afraid to push it into the higher % rates.
Like someone else has mentioned, interval training can be very effective at raising fitness, its all great for mixing it up and prevent the running from becoming 'stale'. Another advantage is that it teaches you how to run faster, sounds silly but there is a technique to running fluently at speed, interval training will help you find your own tecnique.