QPainter::drawPolyline() is dramatically slow on Windows with Antialiasing enabled

I have been doing some further tests of the polyline drawing using the raster engine because my customers are complaining about line drawing performance.
I created a harness in Qt and tested in all versions from 4.4.1 right up to the 4.6.0 tech preview and observed the same results.
The conclusion is that there needs to be some serious profiling put on the antialiasing routines.
My harnesss used GDI+ as an example. I plotted long polylines using the raster engine and GDI+
Here is a typical benchmark.
Take a 1000 point Polyine with GDI+ and Qt's DrawPolyLine routine with Antialiasing switched OFF.

GDI+ - 94 Milliseconds
Qt - 78 Milliseconds

All my tests clearly show that Qt is outperforming GDI+ in this area.
Same points but with Antialiasing switched ON

GDI - 172 milliseconds
Wait for it...
Qt - 10062 milliseconds

Thats a whopping 10 seconds. All tests where conducted without having to clip lines (I wanted that out of the equation because apparently there is a bug regarding long polylines and clipping)