Not really much more to say;
Of several computers available for use, these are two of the larger ones; one has 2x E5-2670, and the other has 4x E5-4640. The problems we're looking at essentially boil down to large matrix diagonalisation problems (i.e. i have been dealing with 125K rank matrices, and in the past have looked at larger ones. Both sparse and non sparse, using PARPACK).
All intuition would tell me that the Quad CPU 4640 should be much faster, but it's not, and I can't work out why at all. Both have hyperthreading enabled, both have 250GB ram.
Could it be that the gains from the parallelisation of PARPACK beyond 16 cores just start to diminish, and are not worth adding the additional processors due to the increase in inter cpu communcation required?
The codes are written in fortran if that makes much difference.