I'm a veteran of Couch 2 5k, I most have completed the programme about 5 times, and then I always lapse and have to start again 
I'm on week 6 currently (20min straight run) and currently running at 7min per 1k.
I really want to get to running 5k in 30 mins as I've never achieved that before, I can get to run for 30 mins but too slow to complete 5k.
Am I better:
a) Sticking at 20 mins and trying to run that faster before increasing the distance or
b) completing the programme and run the full 30 mins, then drop down to 20 mins to increase my pace.
I'm determined this year I will run 5k in 30mins!