I've used Millermatic 350P and like how it works... Simple

I still think FCAW is more efficient and easier to run than large diameter solid wire.

Running Spray transfer with 1/16 solid wire is going to leave you with a giant pool that can only be run in the flat position, big risks of undercut at the high voltage required and sidewall fusion conserns with the tendency to overlap.

I think you will also need to look at gun upgrade on the Millermatic 350 if your going to go through with the Big wire.

Look closely at deposition rates @ 350 amps for both solid and FCAW...

With 0.045 FCAW gas shielded you can get about 16 lbs per hour at  335 amps

With 0.052 FCAW gas shielded you can get 16 lbs per hour at about 375 amps

To get 16 Lbs per hour with 1/16 Solid wire you will need over 400 amps.  350 amps will only yeild a little less than 13 lbs per hour

With 0.045 solid wire you can get about 14.5 lbs per hour at 375 amps

Wire diameter does not always equal effeciency.

they must be pretty good because our shop just got 20 of them the other day.