I've read The Lore of Running cover to cover, Lizzy. Yes, really, I'm THAT sad! What I'm looking for isn't there. Maybe it doesn't exist, because I suppose what I'm looking for is a quantitative assessment of the minimum level of performance that someone who isn't a natural born runner (like me, for example!) could reasonably say, "THAT is as fast as I can run."
Which would mean doing research and collecting statistics on runners who are training hard but are never really going to be good enough to be of national or even regional interest.
And yes, there are loads of internal and external factors that will impact on what we can achieve. And lots of reasons for choosing not to chase one's genetic potential in what, for most of us, is an intrinsically pointless hobby.
By "appropriate training", I mean appropriate running training, treatment and rehabilitation for injuries or for medical conditions (such as asthma) which could affect running performance, and adequate nutrition. Anything else is very tiny print.