( disclaimer: racing sim fan and real world hot rodder here - i'm down to four cars just for me, with a porshe 944 being the slowest )
graphics should not cover the car, it can interfere with visual cues of attitude and momentum.
the player will be focused on an area +/- 15-20 degrees from center. the faster, the narrower.
gauges should fall just outside this "attention fov". they should be readable without looking away from the vanishing point.
as ashmann says, below the car makes it a heads down display, not heads up. only testing will tell if its close enough to the "attention fov". like him, i think i'd favor graphics above / beside the car.
as for the look of the hud, #3 looks very trendy, console, NBA2K'ish. not bad overall. but not exactly classic hud design. but it might fit well with the futuristic look of the game in general.
something about the triangles in #4 just turns me off. perhaps because its not instantly recognizable as to what it is. what is it anyway? i'm not bothering to read the fine print. if i need to read fine print, the gauge is not intuitive enough. bad designer - no twinkie! <g>.
#5 is a more classic hud design. pretty much everything is instantly recognizable. with 1st place vs 1st gear being the only question. and 1 minute of gameplay will answer that.
whatever you chose, the gauges need to be naturally intuitive.
#6: icons are not necessarily intuitive until you learn their meaning. i should be able to jump in this car and drive, not puzzle out icons like i'm learning truespace or blender. <g>.
but visual cues of overheat coupled with a warning - which #6 seems to show - is a good thing.
#7 seems to be a less intuitive version of #5
#8 captured alien spacecraft - all in a alien tongue? kinda get that feel from it.