Usually see people run 1.5 .250 for the panhard
1.75 .120 should be fine for the upper link. It only sees compression and tension. As for the panhard, I wouldn't even think about running 1.25 .120 wall. Sleeve a piece of 1.5 .120 over it or something. They see way more force than you think.
I plan to run 2" solid aluminum for all my links on the new project.
Benz Buggy and Walle Crawler both have had 2" 7075, but 2.5 wouldnt really cost me that much more.
Panhard=Widowmaker. Over build it.
All a panhard sees is tension and compression, just like an upper link.