Coe didn't like 5000m though he wanted to have a go at it with "proper" preparation. This was scuppered after 2 attempts: 1) Winter of 84/85~ picked up injury which prevented him doing the necessary longer endurance sessions in the early Summer. 2)Winter 86/87~ foot injury after 1st race in May wiped out whole season.
As a result he decided to stick with 1500 for 88.
Coe really wasn't built for XC and though he used it for strength as a teenager, run much better on the roads.
Horwill is quoted as saying that he could run sub 13:20 anytime on his 800/1500 training, so he would probably have the potential to run close to 13 mins if he focussed on it for a couple of seasons. Remember, he beat Coghlan, Mcloud and Brendan Foster's 4 Mile course record in 78 (when mainly running 800s) and beat Cova and Bordin over 7Km in '80 and '83 respectively.