If you can fit 120mm fans it would quiet down the noise somewhat as you can get the same CFM's at a lower RPM!
Also consider some form of dust filter on any fan sucking air inside the case, they can get quite dusty inside if left a long time. Some new cases like the Thermaltake
Kandalf case use 120mm and 90mm fans as standard (but no dust filter!), 80mm fans are becoming less desirable.
I've yet to see any firm addressing or producing 'dust free' cases though, anyone know of anything in this area?