What is safer on the street? A 3 point belt, or a 5/6 point harness with roll bar?

With a 6 point bar as pictured you actually could have the best of both worlds. You could have the 5/6 point harness AND install factory type 3 point shoulder / lap belts. So why not do both? You'd just have to pass the lower belt under the side bar, but if you use a swing out bar that's not a problem either.

Sounds like the way to go maybe!