you'd want to run the air pressure higher, the reason the tire in the 205-55-15(listein in michelins mast fitment as a plus zero optional fitment) costs more is a few reasons:-less made(it fits less cars, thusly less are made, the price per unit manufacturing wise is greater..)-higher performance tread compound (again making the manufacturing costs greater)
there ya go

good choice in tires, I woulda bought the 205-55-15 though.... AZ hitman loves his 512's-chet