its not just about amps, more on matching wire size to power levels, turn a high power machine up too high and it just sprays metal over a joint giving next to f/all penetration, the only time a high power machine has any advantage is in duty cycle, and when it comes to welding cars and trucks up this can be pretty much ignored with any machine capable of running up to 160a with .8 wire, main thing with mig on rusty crap that you get on cars is cleaning down to good metal, and doing that without removing most of what was fairly sound in the first place, when I was at it I used two angle grinde