I've discovered that the .045 wire allows the penitration I need but the heat range is not wide. The tab in slot give most of the required strength. The 3/8inch penitration is enough to keep the plates together. It's a strange project, that doesn't allow much discussion. Preheat to 350 gives too much heat and begins to effect the amps selected. Increased amps melts the wire too soon.
Preheat to 180 seems to stablize the pass.The material I'm working with is REAL strange plating, not the standard stuff. can't say much more about that.

Next try is .052 just for the giggles. Thanks for the input and interest guys!