Spanky can correct me if I'm wrong, but from what I think he's saying is that adding more content does nothing to performance on maps that don't get changed.
Exactly. Like I said, we can add 50GB of textures, meshes, sounds and other goodies but performance on Bridge, Urban Assault and the other maps will stay the same. Adding stuff doesn't affect the game's performance, it only affects the performance of the map those assets are in. In the case of AA3 maps, they're going to be problematic because it's tough to get a modern map to perform and look properly on an old engine (especially one that only uses a single CPU core).
This was the first public release (it's a beta) and before now, we've only tested on a dozen or so computers so the information we're getting now is incredibly valuable and the next release will be much more refined.