its just for a typical game level it would need ~ 100 times more geometry and bigger environments.
I guess I already wrote that before but all major engines so far rather specialized on rendering unique (texture baced, non symetrical/ instanced,...) objects. That's nice for product placement but will suffer from more complex interaction or scenarios.
I personally though that with the screen FPS rates we saw so far in demos it would be possible to create a 3d racing game similar to destruction derby 1 & 2 but what makes most of them useless it the way scnery is handles- or I simply haven't seen a demo that does that well. Because all I have seen were rater some smaler scenes or objects.