My machine base legs look like 4080, but they are actually 1.5" x 3.0". Short story: I was able to get a deal on extrusions from a friend, but he only deals in standard, not metric. I had the choice of going with the 3.0" x 3.0". At the time all I was thinking about was weight not wiggle. I think if I were to do it again I'd go with a bigger profile. This past weekend I added some 1.5" x 1.5" gussets at 45 deg. in the upper corners and has helped a lot with the wiggle.
Another option to consider if building a light frame would be to "sheet" (plywood, ABS, etc.) the sides. I think that would really lock it up solid.
-- Bernie