[Darylb]

How does the stiffness wrt sideways deformation compare to the 80x40 pieces?

80/20 1530 series extrusion bent about the weak axis is about twice as stiff as 80mmx25mm bar (0.483 in^4 vs 0.262 in^4)

EDIT: oops... i just realized you weren't comparing it to the 80/20 pieces many designs use for the uprights. To answer your question, the stiffness goes up with the height^3 therefore the stiffness is about 4.1 times greater therefore deflection will be reduced by a proportional amount.