Any best practices on minimizing system performance impact during emerging?
You could always use a different system to do the hard work using distcc: http://www.gentoo.org/doc/en/distcc.xml
you can set the variable
PORTAGE_NICENESS in the file
/etc/make.conf. it sums up a nice value to the emerge process, so that it has less priority on the system. for example:
the above line, in
/etc/make.conf, will make portage increment 10 to the default nice value for that process (this will not set the nice value to 10, it will increment that value).
Try cpulimit. It limits cpu usage per process. So, you can tell emerge to use only 10% of your cpu resources.