Believe me, I agree insurance companies are vultures. But I've bought way to many cars lately and swapped between trims etc. and was surprised how little difference there was.
What far too many people in this thread are ignoring is the fact that there's far more at risk here than insurance premiums or even the value of your car. If you get into an accident that in turn cripples somebody or causes tens or hundreds of thousands of dollars of damage to somebody else's property, then you may be liable for the damages. Insurance exists, in part, to cover the financial consequences of such an incident, not just to cover your own losses. If you don't communicate clearly with your insurance company about your car's capabilities, then they may use that as an excuse to rescind your coverage and deny a claim.
I just don't understand the reluctance of many people in this thread to pick up the phone and call their insurance companies on this point. It should take just a few minutes, and if the insurance company says you're good to go, great; you've merely wasted a few minutes. If they say they require more money, then you'll spend more money; but you'll know that your insurance is valid. If you're afraid of paying a little more money for insurance, then you should be really afraid of having your insurance policy rescinded over a failure to disclose a performance-enhancing upgrade, should you get into an accident.