FC="gfortran44" ; export FC;
F90="gfortran44" ; export F90;
The SAM MPICH test runs after recompiling with F90 support using gfortran and in fact it works fine on SL4 and SL5. So that was not the issue.
message size transfertime bandwidth
32 bytes 0.000000 sec inf MB/s
2048 bytes 0.000117 sec 17.476267 MB/s
131072 bytes 0.001445 sec 90.687654 MB/s
8388608 bytes 0.078437 sec 106.946397
It turns out that MPICH just doesn't work when compiled with gfortran43/44. Leaving me in a bit of an pickle as CASTEP will not compile on SL5 with gfortran, you have to use gfortran43/44!
Time for the backup plan ..... openmpi.