Resting heart rate is relative and not a precise predictor of performance. My lowest was about 31 bpm when I was at low 14 5k fitness. At sub-14 fitness, the rate was 32-34 bpm. My roommate who was a 13:19 5k guy had a resting rate of 48 bpm. Generally, the better shape you are in, the lower your own resting pulse will go. And tracking the rate can help you determine if you are overtraining (a higher than normal rate in the morning may mean you are training too hard).