It’s not a 4mm burning box. It’s 60% duty is a shade over 110 amps. You’ll run 1 off 4mm rod and you’ll have to let it sit and cool for a bit. It’s a 3.2 box. They are ok machines but they are still a budget machine. You’ll find you give it a hard life if you start getting into hot 3.2 and mid range 4.0 settings. Up to you but I’d be buying a 200 personally to ensure I’m well covered.I think i will go with the termal arc 175 them seem to have a good following . Have you burnt any 299 rods or cast .