This is Floris mod right?(click to show/hide)
I liked how bandits were a proper organised force and was a real problem. Once, I even have to forget about capturing a rhodok castle in my siege campaign just because some bandit leader was blocking the passageway. I must say I was a Swadian Marshall and had 5-6 lords following me, and I was commanding more than 100 men as well. I tried battling with them and even beaten them, but in the end there wasn't enough men left to conquer a rhodok castle.
With 100 to 200 heavy cavalry units (swadian or sarranid is best), you can dispatch those 800 bandit armies very easily. Maybe not in floris mod though.
Also, bonus because with all those prisoners you can replace your losses without paying anything, and they make them move very slow, which means you can select your fights.