I used 1 3/4 x .120 DOM.... and lots of it... center windshield to dash bar (Earnhart Bar) as well as 3rd roof bar, and Petty Bar and tubular 1" x .120 DOM gussets at every tube junction. over 24 of them.
So I am OK with 1 3/4 x .120 DOM ... 1 5/8 x .134 DOM would also be very strong,,, the wall thickness is a plus,
However,,I am not sure which is stronger 1 5/8 x .134 DOM or 1 3/4 x .120 DOM....
Cage and Chassis construction and design also have a lot to do with it, not just the differance in material.
Charles