Maggs
As far as GTAW or GMAW goes, the operator will not see much if any difference between T6 or Zero conditions. The current, voltage, WFS, weld pool, etc. will not be noticeably different.
You may or may not see a difference in distortion control.
There will defiantly be a difference in mechanicals... But you did not ask about that.
I doubt the welders will be able to tell the difference.... But you should do a trial anyhow.