like I said I know little to nothing about metal but my local club bought a $1500 chunk of ar 500 and decided to cut it themselves to save money and you can shoot through them like they were butter. Pretty sure they used a normal torch though and welded bases on to stand them on a rail. I read that plasma is better but will still affect the edge in a way that a hit will damage the target quite a bit compared to the area not affected by heat. However hits to the edge should be minimal compared to the middle area.
But that is just stuff I have found while trying to find targets and researching metals. I have no experience or first hand knowledge to back it up.
Jason