Mild steel will give and bend (absorb) when hit. CM will crack over time, the reason for the X-ray requirements. My first car was MS but was hard to sell, the two I have now are CM because that’s what the racers want. Remember the number one rule, triangulation. Your 50 pound head in a 5 pound helmet flopping around to close to a bar in a wreck is not good. I don’t think 2” is far enough away, remember Dale Earnhardt. these are just my opinions.
That is almost true, aircraft of yesteryear were mostly chromoloy and were welded with a torch, the heat affected zone was a lot larger back then and a 3/4" .049 wall tube in a cluster weld could survive an impact at 100 mph plus. Modern welding uses TIG and the HAZ is a lot smaller, if you pre and post heat and not contaminate the weld with the tungsten, it will last just as long as mild steel and look as beautiful as a modern weld. Tim
