So it doesnt matter the number of CRATES, but it works on the number of GOODS. Have I understood?
Yes, that is correct
If i've got 450 goods (300 crates), 300 men, 300+ fast horses, at what speed does my army travel?
You have got more goods than horses and more goods than troops.. So your speed will be reduced.
At a guess I would say you will be moving somewhere around 8-15 m/m
If you had 450 horses you would be moving around 30-35 m/m
Based on you traveling across the plains (brigdes, mountains, hills, forest will all be slower)
As far as I'm aware no one has developed a speed calculator, so I can't give you exact values. (Too many variables)