Anyone who is going to back Kemboy needs to think of breeding. Nothing has been made of it but I've had this in my mind for a very long time. His sire Voix Du Nord has never had a winner in a top class race beyond 3 miles. There are a couple of exceptions in Vroum Vroum who won a 3 mile Mares hurdle at Ascot but she beat trees and outclassed them off a fairly slow pace.
You look at his progeny, Vibrato Valtat, Taquin Du Seuil, VVM and such like, and you go through his progeny, it will point you to intermediate trips with their optimum distance being 2m4 to 2m6. They often fail to stay the trip in high class, big field handicaps and if there's pace in top class races they are often found wanting beyond 3 miles especially in top class courses too.
Unique De Cotte was probably the rare horse who finished 2nd in the Pertemps in the UK a few years back and he came from out the back off a slow pace that day, so you get the odd exception but I've seen over the years that his progeny do not get the trip in long distance races and I'd be a huge place layer of Kemboy in the Gold Cup purely down to this fact.