Using each wr holder for comparisson just doesn't seem right.
And using non rabbited races (aka championship races) is equally wrong.
First because El Guerrouj was a very complete athlete and probably could run about the same as Gebremeskel did in Paris 2012 given a few more attempts.
And even if a championship race is quick (the one in 2003 was actually very fast) whoever is leading is going to be more taxed than whoever is following, and at that level where the competition is very balanced it matters a lot.
Thirdly, these guys in question can obviously perform elite times (enough for Olympic/world standards) from 1500m-Marathon.
Down where on the average runner world, in a 5000m race (doesn't need to be overly quick), a 10000m runner would probably have an advantage over a miler, especially if the miler also runs the 800m frequently.
The 5km and 10km aren't really that much different (in the systems used that is).