I ran a test using openmpi-1.0.2 on OSX vs mpich-1.2.6 from mryicom
and i get lacking results from OMPI,
at point point there is a small drop in bandwidth for both MPI libs,
but open mpi does not recover like mpich, and further on you see a
decreese in bandwidth for OMPI on gm.
I have attached in png and the outputs from the test (there are two
for OMPI )
Center for Advanced Computing