A convenient practice is to maintain one .gracerc file in the home directory, which contains all options necessary for the whole platform (possibly querying the hostarch ECLiPSe flag). If some programs need other options, they can be modified in local .gracerc files, which first compile the global one and then make local changes.
Write your program cleanly, using matrices and lists and operations on them wherever possible. Remember that defining and setting the constraints may represent 90 % of your source, but it represents only a small fraction of the execution time, so it pays off to keep it clean and well-structured.
(to be continued)