Hard versus soft NFS mount - shared middle tier.

Does anyone know of documentation or have experience showing the best way to set up the middle tier on NFS? I"ve had complaints on performance but can find no difference in performance when reading or writing files to an NFS share mounted with either the hard or soft option. I use the "time" and "dd" commands to write and read files and the results are fairly consistent. This is really frustrating because from the AIX level it looks good but it takes forever to log into the application when the hard mounting option is used.