Geez Falcon, 5.6 million polygons.. you're aiming for extreme highpoly models when you work. But then again with your great hardware that's understandable. You should do one single mesh within Zbrush 2 instead that has 6 million polygons and let Maxwell have a go with that one. Do a head or something..

The method of compositing stuff together is good, i like that and i got nothing against that at all. I sometimes do it myself if it adds to the final look of the scene.
And if you don't mind hehe i'll be pointing out stuff yet again, i'm sure you're used to it by now

sorry
The detail is great, no doubt about that but unless you render it poster sized the detail won't show up in the final rendering, doing it monitorsized it'll never show up as much just dissapear and it's too tiny to show up or it's in the shadows or something else. Utilize LOD to shave off poly detail that won't be visible in your final rendering, that saves you time, cpu and ram

I'm missing some grime and dirt maps on the robots and weapons, perhaps some specular maps too.
I apologize for being picky

but i think it's important or else no one learns, not you and not me and not anyone else either. But it might bother people tho.. heh
/ Max