Since you are mentioning it as a 330i, I am assuming you are considering a sedan(both e46 zhp or e36 m3).
As long as its a sedan, the insurance is going to be cheaper for you. M might be higher than 330 zhp sedan, but you will have to talk to the agent for that being much older car.
But as soon as you get it in a coupe, its considered a sports car so the insurance goes a little up. My point is, insurance for 330ci is going to be more than 330i. May be the insurance on 325ci is more than a 330i zhp. And most companies do not have an option for performance package for 330. Its either 325 or 330, so no zhp option.
Whatever the case is, you should get full insurance. Do not skimp on insurance on these cars. These cars are expensive to fix if in an accident.