Draco, as far as I can tell MP will always drop below 100%, regardless of how your settings or performance profile is. The only difference you get is how long it takes to do so and how far away it gets from 100%. The first win i had in MP was in normal caps, and we 4 or so literally threw everything at the homeworlds because there was so little gamespeed left we could barely see what exploded.
More recently, we've got a low-caps 50-planets game running fairly well with 3 people at ~80-90% gamespeed, one step below average.