integer qHash functions are far from ideal

When trying to implement a 3D space hashing object in Qt (4.8.1) I noticed performance issues when using QHash with 64bit integer keys. The keys were a simply mash up of the x,y,z coordinates of an object (x<<32 + y<<16 + z) where (x,y,z) < 65536. The best I could achieve was ~800,000 hash insertion per second (2.2GHz i7 laptop, OpenGL rendering was being performed as well). A QMap implementation was actually faster despite O(nlogn) vs. QHash's amortized O(1)!

I used a custom hash (MurmurHash3) for my objects (using the same source keys) and have over doubled performance. This leads me to believe that Qt's qHash algorithm for 64bit integers is terrible, resulting in far from optimal hash performance.