I haven't used it. Downloading now (504 MB)!
http://www.studiogpu.com/From their site:
" MachStudio Pro is stand-alone, visualization and rendering software
that lets 3D artists create and manipulate lights,materials,
and HDR cameras in a real-time, non-linear workflow environment to achieve film quality results.
MachStudio Pro system requirements
Operating System: Microsoft Windows 7 - 32 bit or 64 bit
Microsoft Windows Vista Business - 32 bit or 64 bit (SP1 or higher)
Hardware Minimum Requirements: Intel Pentium 4 or higher, AMD Athlon 64, or AMD Opteron processor
2 GB RAM
2 GB of available disk space
1 GB DirectX 11 compliant video card (tested w/ ATI and NVIDIA)
"