I just found a really impressive set of tools over at Running For Fitness.org.
There are really useful for working out, for example, the pace you need to run to achieve a particular distance, speed, VO2. I'm using it to calculate my rates I need to work into interval and tempo training.
It's not that I'm already undermining my previous post about not trying to achieve a personal best time in Oslo this year. I'm not. I want to be stronger and that requires raising the bar, as much in speed as in endurance.
Try the tools out - they are proving really useful.