I use 5356 to weld 6061 to 6063, 4043 does not weld all that good to me on 6061. I have repeatedly tried 4043 on both the Syncrowave 250 and the 250 EX, never being completely satisfied with the finished weld. The only thing in common between the two welders is the coolant is distilled water. Miller does say the water should be deionized water, Miller also says the high frequency can bleed into the arc if deionized water is not used, this may or may not be why 4043 does not weld very good for me.