It's confusing for me too... I guess it's :
50 men, 50 horses, 50 crates - 75% (to 40% with less horses, and if you have more crates than men you have more penalty.)
50 men, 51 horses, 50 crates - 85% (i guess you can have 0 troops)
Btw, which horses are considered slow, and then what speed with crates (85/75%)?