Having notice people say about distance races, but being raced at 1400, or 1500; I think it doesnt matter the distance the bird is flying, I dont think they know how far they have to fly to home, could be 50miles, could me 500, the thing is time on the wing.
If you have a stiff race from any distance it will be the birds which are most comfortable at flying at the fastest possible speed in those conditions which will win.
Dont think I explained that too well , say 300 miles, a sprinter comes out the basket and flies 50mph, and can can only keep this speed up for 4 hours, then flies much slower (fatigue); a different bird comes out and sets at the 300 miles at 40mph and can go on for 7 hours, until he too tails off that speed (fatigue). [so what is the convoyers shoe size - reading it through it sounds like the Pizza Hut advert ]
Lets say a strain of distance birds are the ones which ideally fly at 30mph and can go on for 16 hours, and a strain of sprinters can do 50mph for 6 hours, given the prevailing conditions either bird could win at almost any distance.
What I'm maybe trying to say is look at the hours on the wing of a race, not the distance or velocity, to see which are the sprint, middle and distance birds