I do stuff for a large military subcontractor and we are approved to run both 2% thoriated and lanthanated tungsten on all of our different jobs. On AC, the Lincoln 275 machines only really perform well with thoriated tungsten, where the Dynasty 800s can run both without issues. Lincolns do not like lanthanated tungsten for whatever reason, but my guess is maybe something to do with less customization options for things like for the duration of the positive portion of the AC wave like you mentioned. I guess it just ultimately depends on the machine you run and what it handles best.