In reply to Game of Conkers:
Ok I get you. Looks like you've got it sorted then running 5/6 days a week with all the right sessions in there should have you coming on nicely over time.
From personal experience and from others I've trained with hitting a decent spot of form can take 12 months of consistant training two years being the real aim. Consistancy being the key and progressing your sessions making them harder and harder. Increasing speed and duration and decreasing recovery over the weeks and months.
I guess like you said core strength is something you could work on but unless this is really poor I don't personally see any correlation from when I have awesome core strength to when I do not possess these powers in my running ability. I run best when I have trained most which is incidentally when I hav climbed little and therefore am weak due to little stregth training.
I think leg strength is best improved through hill work and cycling, this way you can kill two birds with one stone by increasing base aerobic fitness. I you want to do gym work for general conditioning or aesthetics then great but if you want to get as good as you possibly can at running use the time to run more.