Dan, a friend of mine did all the mig welding on my 56 front clip with my 150 Miller with no problems. It can handle up to 3/16'' possibly even 1/4'' single pass with no problems and has a nice, small compact gun.
I didn`t see a need to go any bigger for most my welding jobs.

 

At work we got a Lincoln 215 amp and it will only weld 1/4 in a single pass. It can do 1/2 with multiple pass with flux wire. A 140 amp model can do 1/8" in a single pass and most are 115v.

The 180 will weld 3/16 in a single pass.

 

So I shouldn`t keep welding 3/16'' with the 150 Miller?