wouldnt 5 be needed for a car game any way? (4 tires and one body) i think 5 inc ommercial would eb great because this really gets users interested.
example: if some1 was to build a racing game they coulld start making the game with one car only for testing. make an aawsome game around it and see that the physics engine is exactly what they need and upgrade to pro to add other cars and objects. would also be great for a personw ith com. to make a techdemo for their game.
a car game is not the only example but i think 5 would be most suited because with 5 you can expierment and see if you actually need thw full physic engine. this may be bad for conitec a little, but at same time be good.