My 5K Pb is around 30 minutes - I say "around" because my absolute PB of 29:40 was over 2 years ago - while recently I have done 30:40 on a parkrun pacer day. A friend of mine tells me that "I don't try!" at parkrun - and that is true. Firstly, I believe that chasing PB's is the sure fire way to injury - and fundamentally futile. So I have chosen to try to run the 5K "stronger" rather than "faster". I think I have now achieved that after almost 100 goes at it - and it is time to start really getting stronger at the 10K distance.
These longer distances mean more endurance in needed to complete the distance easily - and if pace is a consideration, then more stamina is needed. For me - endurance ( both physiological and psychological) essentially comes from LSD. According to the online calculators - my easy/LSD pace is somewhere between 7-8:00 mins per K. I have always found it difficult to do that pace at the lower end of the scale and much easier to run the upper end of the scale. At the lower end, lower body ( ie legs,hips,etc) muscular/ligament discomfort comes into play and I have noticed that many of my friends will not run at lower paces than what they feel"comfortable" doing. I can certainly understand this - but I think they are possibly doing themselves a disservice by not doing it. I know I have avoided it a lot over the past few years - but lately seem to be a little bit better at it. At the extreme - Arthur Lydyards training ( he is long dead now and perhaps his ideas are not so popular now?) insisted on many months of LSD before running faster workouts.