The only things you can really affect are the lightmap resolution and particle output, and how efficient the streaming is, and whether textures are displayed at max res or not.
All the other stuff is pretty much placebo effect.
That said, maximizing the LOD and particle/volumetric haze and enabling what few shader model 3 effect (especially on the aliens themselves) are actually in the game does actually make a big f**king difference, so does keeping bodies around, even though the joint constraint friction and gravitic momentum on the ragdoll physics are some of the worst I've ever seen.
Half Life 2 has better ragdolls.
That said, there's this:
It does include an altered lightmass, but the hooks are not actually employed as stated earlier, but who knows, if GBX gets off their ass, something might come of it.
Remember to add YOUR Cards's vendor ID to compat, with the right hex.
Also remember to adjust the streaming and memory budgets for what you actually have.
I have 48 Gigs of memory and 4x2 gigs of vram, and that's what it's set to, so change it to whatever you ACTUALLY have, else hilarity ensue, and don't forget to make a forced setting profile on your card's profile library or UE3 will have a tendency to start reverting shit on you.https://dl.dropbox.com/u/16768161/Config.rar
Also bear in mind bodies and gibs are essentially PERMANENT until a new geometry mesh loads, and your memory footprint will grow accordingly.http://steamcommunity.com/profiles/76561197972382074/screenshots/