Ok...

[AgentZero]

I usually set it at 400%. 200 if I'm looking for a quick game. Last time I set out to play a total extermination game, I was playing with in a galaxy that had about 100 systems. I got to the point where I had 31 systems and 3 other AIs had the rest. I'd built massive fortifications on all WPs leading to soon-to-be-enemy territory, mined them heavily and had thousands of satelites over all the WPs as well. My invasion fleets numbered 4800 (and I had about 60 pop transports racing around trying to fill up smaller colonies).
I then launched my massive invasion; 48 100-ship fleets (16 per enemy empire) burst into enemy space through artifically created WPs.
And ran smack into the stiffest resistance I have EVER seen the stock AI put up. I'm lucky I used my own WPs because the largest of the three had the main WP to my space defended by sixteen Starbases! And these weren't your mamby-pamby stock Starbases, either. Each of the behemoths clocked in at 6,000kT.
Anyhoo, I realized that I'd be looking at fighting tactical combat for every single planet if I was to be assured of victory. I then whipped out the calculator and plugged in a few numbers.

69 systems for me to conquer with around 10 planets each makes 690 planets. Call it 650 for arguments sake. 650 planets * 15 minutes average tactical combat = 9,750 minutes = 162.5hours = 6.7days non-stop playing, but since I only average about 2 hours a day game time that worked out at 81 days.

So, to conquer that galaxy would require the better part of three months just counting combat, and not taking into account repair & maintenance, replacing lost ships & troops, protecting conquered worlds, AND running the rest of my empire to boot. Needless to say, I declared a moral victory and went to bed. ;-)