I think when he states bare bones, Nick is not referring to peak performance. Someone coming off CC season might only be able to run a 12.5 flying 100 because of specificity training. He at that time might be able to easily hit 20:00 for a 4 mile tempo. After a training block of mile training, that person would quite easily be down to a 11.5,. I've always been a strong proponent that if you want to break 4:00, you have to be able to run this. Take your 800m flat PR (and this requirement means you're focusing also on you're above and below events , 800m, 3k/5k) during peak season, double it and add 18 seconds (with rare excpetions). I.E. Alan Webb in his best year. 1:43.84 and 3:46.91. 1:43.84 x 2= 3:27.68+18=3:45.68. His 800m is graded stronger than his longer distances this year though. He ran a highly elite field as well in the 800m compared to his solo low key mile AR. As far as 800m possibility. The maximum capability I have always used is a 1.07/1.11 x 400m PR computation. This obviously won't work if you take a pure 10k and run in an 800m. This is referencing a pure 800m runner. I think Nick Symmonds is a great example of the 1.07/1.11 calculation. A 47.2 flat 400m PR for Nick, which he would pry agree he was in during the 2012 Olympic season gives you a 1:42.9.