5k workout said: but I am looking for something that is a little longer
that isn't going to improve your turnover.
to improve turnover you want short, sharp, fast work with long recoveries, with either:
1. high acceleration - jog very slowly with very, very, short strides, high on your toes, then smoothly accelerate by gradually increasing cadence then lengthening the stride. sprint out for no more than 80 metres, then slow down again, jog slowly for half a lap, return to the very short striding jog and repeat.
2. slightly down hill - as Yes but ... suggested, running down a slight down slope is good for increasing cadence. just don't go too far or too fast. turn around and walk back up the hill, then repeat.
3. modest acceleration - run a medium length repeat, like say 300m, then change gear sharply and accelerate hard over the final 100m.
cheers.