OK that's a simplistic generalisation but try and run quicker for shorter distances. This is why people get quicker when they join a club as a coach will include higher speed "repetitions" into training sessions. Really difficult on your own.
As you are getting quicker as you run I have a feeling that you are not in the first flush of youth; if I'm wrong then sorry
What's your flexibility like? Increase your flexibility and your stride length may increase; only a 1-2 cm increase in stride length makes a difference.
Few routes of 8 miles round B'stoke; I've tried to keep them simple. Most of the bridleways west and north of the hospital are great for running but get into the downs towards Ibworth and Hannington and it gets hilly. Get an OS map and plan over a beer.
Avoid A339 and A340 they are not running friendly!