Scale is an interesting issue in games and movies. Right now I'm working on a racing car video. Knowing how much track I need for a given shot is quite important since making the track and road side buildings is pretty time consuming. Not to mention rendering. At 24 fps, a 3 second clip could take half a day to render. Generally in a package like Blender I'll assume one unit = 1 meter in my imaginary world. Then I can do calculations like how many meters can I cover at 100mph? The math to figure that out isn't hard, but the magic of the internet makes its trivial with conversion tools.
So if I want a 3 second shot of a car driving at 70, I need about 100 meters of track. Of course if the track isn't straight then the cars have to slow down, so a tight turn will reduce the amount of content that needs creating, as well as potentially reducing the render time (size of visible set). The first Ridge Racer was very cleverly designed to keep performance up. The track was designed to never require more performance than the PlayStation could provide :-)
I'm trying to render something like this, but with Aliens. And I'm definitely going to steal the engine sounds from this video, and I'm not going to feel guilty because Shell has enough money already. :-0