well Forged Alliance runs smoothly on my computer. Even with more than thousand units I know FA to run with simspeed 5-8.
Demigod even starts right from the beginning with sim speed 3 or 4 with maximum 50-100 units at the battle at the same time. not that this is bad, but maybe people with worse computers will slow down games, and why is demigod slower than FA where much more things have to be "simulated"?