I have a sump on my 180 and my sump is smaller than yours. I only have the mid section on mine filled with bio so basically I've probably got a third of the bio you have and I have never had parameter issues or tank crashes and i'm probably overstocked too! Don't forget you'll have BB all over your tank and sump, not just in your designated bio section. Going off that i'd say you'd be ok with what you have but, that said, everyone's different and have their own views on how much bio media is enough.