My logic about an extra kilo is right but my argument was wrong.
One kilo on the back of a 500 kilo animal don't make jack of a difference to the horses performance.
But once the horse already has 50 kilos on board,that extra kilo then could be a huge difference.
Here's my proof.

Olympic Games - Weightlifting.
We all must have seen it.
3 chances to get the 3 white lights.
Once these huge athletes get close to their limit,the extra kilo or so seems to be too much of a burden.
And the event only takes a few seconds to complete to its finale.
If they had to carry that weight for a kilometre?.It ain't gonna happen.

And if you can accept that then it opens up another form factor that could increase profits.

Weight carrying ability.

I'm sure in a previous life I read about a horses maximum weight carrying ability.Maybe in Rem Plantes' book.
Once a horse gets handicapped to a certain weight,he stops winning in those types of races and is moved up in class or WFA.
How many horses do you see win carrying 60 kilos or more?

So what I am suggesting is that a horse can win a city race with 48 kilos,but would not be able to win an improvers in the bush with 60 or so.

And having associates in the building trade,Kenchar,housebricks in fact weigh 3 kilos,with or without holes.So if your bricks are weighing under a kilo on your scales,I shudder to think how much you would weigh on a set of accurate scales!.

6 x 80 = 480kgs.AWESOME!

And Dingoboy.You never cease to amaze me.