I'm an average runner. I can churn out a 7 min road mile fairly comfortably over, say, 5 miles. If I run a faster tempo style pace I can maybe do 6min 50 secs (I do 95% of running on fells so don't know absolutely precise times). But I'm wondering if it is possible for the likes of me to be able to run a 5min 30 sec pace like the 'speedsters'? What would I have to do to achieve this? Or is there a limit to which a mortal can go? Has anyone ever trained so specifically and intensely that they have become significantly quicker and, more importantly, has this ability to run a fast min/mile pace on the road helped when on the fells? Thanks.