If you're still getting excessive fireflies that don't go away after a few hours you should experiment with other surface integrators and change the pixel filter to gaussian.

I had a scene this weekend which wouldn't clean up, even after 8 hours, I switched the surface integrator from 'distributed path' to 'direct lighting' and the scene cleared up completely in 2 hours.

Software: OS X 10.8 - Poser Pro 2012 SR2 - Luxrender 1.0RC3 - Pose2Lux
Hardware: iMac - 3.06 GHz Core2Duo - 12 GB RAM - ATI Radeon HD 4670 - 256 MB