Until now I've only played on Immense maps with standard settings with no problems;
I guess that if it gets really crowded I'll need to extend the 2GB limit.
Thanks for the link Gaunathor, useful little tool there.
On a side note, is the immense 22x22 the maximum GalCiv2 can have?
Or some mod allows for even bigger maps?
Edit:
it seems "Immense" is as big as it gets, still not sure about some mod though.