Well, there are some practical downsides to the beefiness of SE5.
25 megs of
(beautiful) combat replay. For a 50 ship/150 fighter warppoint assault in GGmod.
Then next turn, 75 more megs of combat replay... Of the survivors chasing fleeing ships that they have no chance of catching, since they have the same speed, and the combat map is infinite.
The turn after that, I ran out of hard disk space... so there was no replay saved.
Compare to SE4, where five megs of combat replay takes only an hour to create, and involves upwards of 700 ships / 10000 fighters.