I'll meet you half-way. Some of the things that system-limits.PL probes for are specific to your version of perl, and some things are specific to your system. I've got system-limits.PL producing two files now, one of them for system specific settings. These settings can be reused when you build Forks::Super on the same system but with a different version of perl. The system settings take up about half of the time, so running Makefile.PL the 2nd time should take about half as long as the first time.
"make clean" no longer removes the output of system-limits.PL. So if you build Forks::Super on the same system with the same version of Perl, system-limits.PL won't have to do anything.