JF, just as an idea, how about dropping your pace/ time goal for a couple of months and focussing just on increasing your weekly mileage instead? Pace goals can feel a bit 'all or nothing' and can leave you feeling frustrated until you achieve them and then hollow afterwards - the satisfaction can be short lived!
How about just focussing on your running form, cadence, economy - whatever during at least your long run instead? Drop your focus on pace for now. After a month or two, do a time trial and see how you get on! 
Edited: 15/09/2012 at 17:15