This is for My home shop. I would not be doing any pipeline or certified work.  Materials : aluminum, carbonsteel, stainless steel, tig brazing. I have a 600 amp sine wave machine now, certainly don't need one that big. I used to have a friends Dialarc 250 HF, I used that at max output at times. A 250 amp machine would likely do 99% of what I need. I would like to be able to handle 3/8 material, but still have good low end performance. I use a MIG spoolgun for aluminum when speed is more important than quality.