Some motherboards are reporting unganged as single channel at boot, this is not true, if you see anyone saying they have defective memory please point them to this post.
Ganged will give higher sandra bandwidth at this time than unganged, this is because sandra does not fully support phenom and is working in 1 thread mode. Once sandra supports Phenom unganged 2x64bit will take the lead
If you are running multi threaded benchmarks you need to be in unganged mode, this is the fastest way of running the system.
Crossfire and Hybrid Crossfire are different approaches. Hybrid would suit him better than a 8600GT, I guess, since he's already going for a 780G mobo and could save some power by using Hybrid [while increasing performance in a scenario of need].