Paul - I ran Eastleigh last year in terrible conditions, but even then it was still a good course. Only 1 hill in it, and it's early on (somewhere around 3-4k if I remember rightly), so you'll have it out behind you whilst you're still fresh. What is your typical training week like at the moment?
For any distance from 10k-mara, imo, the most important session is a proper threshold/tempo session (i.e. pace between current 10k and HM - obviously as you get fitter this pace will improve, so unless you're racing you'll have to judge the appropriate pace yourself, or use a HRM, but try not to start generating lactic - the purpose is to nudge up your LT from below), so a pick from 5-10 x 5mins w 1 min walk/slow jog rec, 3-8 x 8mins w 2mins jog rec, 2-4 x 12mins w 3mins jog rec.
You may find it easier to maintain a consistent pace on the track, and you should also start in at the lower number of reps of each of the above sessions to allow room for progression. If you decide to use them, plan it based on the total number of minutes you would be running at threshold for each time, and look for a continual increase. Preference would be to do it by HR, rather than pace though, and initially, you may find that your pace tails off very quickly for the HR, but don't worry, it will pick up in time. Hope that helps.