I finally got a new system specifically built to do some serious real-time path tracing tests. It contains 1 quad core Core-i7 and 2 GTX 580 GPUs and it just rips through the most complex scenes you throw at it. Brigade 2 doesn't use the CPU for rendering, but it is important for dynamic scenes that require multiple BVH updates/rebuilds, which is currently done on the CPU.
The Brigade 2 path tracer can really show its muscle on such a powerful system and regularly breaks 250 million rays per second as can be seen in the following video of a real-time path traced building containing 430k triangles (640x480 full render resolution, 8 spp per frame, motion blur with frame averaging):
Color bleeding from the floor on the overhanging structure:
Orange color bleeding on the disk shaped roof:
The building model is free and can be found on http://www.3dmodelfree.com/3dmodel/list475-1.htm (requires 3D Studio Max). The next logical step is to build a street and eventually an entire city, in which you can leisurely cruise around GTA 4 style. It's perfectly doable, I'll post some screens and vids soon. Photorealistic gaming, it's just around the corner :-)