It's always terrible when an accident occurs. The only issue I have ever heard against my stock seat harness setup was the fact that they hook a bit lower than most people's shoulders and there would be a compression of your shoulders (because of the squeeze effect) in the event of an accident.
I honestly don't care. I (personally) firmly believe I would be so much better off with my harness than with a seat belt in a wreck. And if I HAD to pick death or paralysis..... Well lets just say that i would get to see my family the rest of my life.
I don't "think" that you would actually have this happen due to all the give in the seat bottom and the fact that most people don't tighten themselves into the harness till they shut off blood flow. So there is some give in the harness anyway.
Just do what you think is correct. And if you want to raise the connect point at the top you can buy the bar that Bert's sells. I will stick with mine and be happy with it.