On the Carbide, or Cobalt question: Cobalt will drill a Grade 8 bolt pretty easily, so should think it would do fine on an insert bolt. The only thing I've ever really needed a Carbide bit on was a loader bucket cutting edge, that I made into mount for a bolt-on cutting edge. The bucket edge was hardened on the outside, but once through the surface, it went right through, using a magnetic drill press. Cobalt didn't last through two holes, on that job.