Hi puffy, everything comes down to the heart rate whether people choose to train by it or not! It all depends upon how serious and technicall/scientific you want to be.
If you like I could send you an excel spread sheet or simple text document with training paces aimed at your ability now, coupled with some faster interval sessions and suggestions on how far, how fast and recovery times etc.
Give me some background on the kind of milage you're doing each week and sessions you like doing?
Regards Paul