Take a look at these 2 articles. Seems the pros use Grade 8 fasteners. Here are two articles I found with useful info from the racing community in CIRCLE TRACK.
http://www.circletrack.com/safety/ct...ide/index.html
http://www.circletrack.com/safety/ct...unt/index.html
Based on my research so far, I am leaning towards the Schroth 4 point belts for my Cobra for street duty only. If you want to see the R&D that goes into their belts, check out their web site too, cool stuff.
Bill