I guess my post was vague.
Typically on track you have a helmet and neck support and other protective clothing.
Not so on the street. Even without a helmet your head is a good chunk of mass floating around on the end of your neck. If you where to be strapped in tight on a city street/hi way and be involved in a major accident the six point potentially can do more damage than protect without the additional safety gear. I also don't believe they are not legal to use on most public streets.
Personal experience...
Stock seats and stock three point belts in a sideways accident in a viper, at a moderate speed it was extremely violent inside the cockpit. I bounced off everything inside the car before it came to a rest. I broke 3 ribs and bruised my driver side kidney.
Very very similar accident in race buckets and 6 points, albeit the object I hit was smaller, the only thing that wobbled was my head, soft tissue damage in my neck that is still painfull.
I've read about internal decapitation, and if I had been in a frontal accident I don't feel i would of faired very well.
Maybe it's just my opinion, but personally I will never use six points on the street from my experiences