Insane map with about 100 factions will use anywhere from 8-12 GB memory on top of any OS memory being used.  Like Falkoner says if it fails it will fail right away.  Other than that long turn times usually happens with exploration treaties so avoid them as with that many factions and exploration treaties with many can slow turn time down to 5+ minutes otherwise without exploration treaties most of my turns are less than 30 seconds.

I also upgraded from 8 gig to 16 gig. I saw a noticeable increase in performance as well. Multi core processors do well with GCIII. More threads = faster turn times. I play on Insane with 50+ factions. 

So it sounds like it will run under 8gb but performance will suffer?  Just curious, when you guys run with 50+ factions are you using something like Gauntlet's Race Mod for variation?

Nope just use my 50 or so factions I created plus some other workshop factions that I've subscribed to. All my factions use the in game tool and are available on the workshop.

Running on 8gb is possible, but has limits and performance issues.  16gb improves performance on a medium rig for all map sizes and makes insane with many factions possible or more possible, but it does not make up for a medium processor, especially with many factions.  Gauntlets Race Mod does not seem to add terribly to the load and looks as good as Stardock stuff or better.