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

You do realize that the 5" mentioned is not from above the helmet, it is from the tube running towards the rear..

Yeah, I do. And granted that is an nhra published diagram I believe (maybe not given it didn't say TIG).

What I plan on building probably won't be exactly to NHRA spec. I'd make sure my head was far enough away for street driving, both vertically and horizontally.