One S2050 has four M2050s, not two (I inferred this assumption from your 6.5 multiple).
I'd like more information on the CPUs and CPU/GPU bus of this FASTRA II. CPUs are really gaining back a lot of their performance relative to GPUs - an M2090 is only about 5-10x faster than the newer Intel Xeons in a properly multithreaded program that pays attention to the NUMA nodes. This is efficient enough that for large simulations which do not fit on one GPU, running portions of the simulation on CPU easily overcomes the CPU/GPU communication overhead in terms of performance.
I'd like more information on the CPUs and CPU/GPU bus of this FASTRA II. CPUs are really gaining back a lot of their performance relative to GPUs - an M2090 is only about 5-10x faster than the newer Intel Xeons in a properly multithreaded program that pays attention to the NUMA nodes. This is efficient enough that for large simulations which do not fit on one GPU, running portions of the simulation on CPU easily overcomes the CPU/GPU communication overhead in terms of performance.