The radiosity calculation uses only 30 to 60% of my CPU, and only use 6Mb of RAM ?!!
The reason for this is that radiosity uses your 3D accelerator card to render, so there’s little load on your CPU. But no much help for save radiosity calculation time in faster 3D Card, because the bottleneck is Get Render-Data From Video Memory, on the other hand, the bigger scene will not debase performance much.