I'm confused - with the dual CPU/octo-core model, you can get up to 32GB RAM in 4 slots, and they have options for 12GB in 3 slots or 16GB in 4 slots.
Will the machine actually run faster with 12GB in tri-channel mode than it would with 16GB if I don't actually need 16GB and would not be swapping to disk with 12? Any advice much appreciated here.
It's about memory bandwidth. My understanding is that 12GB in tri-channel will provide 25.6GB/s. With 16GB where 12GB is in tri-channel on one processor and 4GB in single channel you'd have 25.6GB/s access to 12GB of memory and 8.5GB/s to 4GB.