@uncle_bob: It is hard to judge but I can put weight on top platform and wiggle it by 1-2mm if I really try. If I had to guess I would say that the wood is flexing and not the pipe. If you use solid 4" PVC or metal with 3/4" flatstock I wouldn't expect any problems.
I was using slic3r defaults. 30mm/s for outside perimeters and 60mm/s for everything else. BTW, I ramped it up to triple that for a while. Of course acceleration didn't allow it to truly triple but the machine was able to hang in there. The outside surface quality suffered but not as much as I would expect. (I would say that all the surface issues came from the lag from the bowden tube.) Bottomline: go as fast as you want but slow down to 30mm/s for the outside perimeter.
I was using slic3r defaults. 30mm/s for outside perimeters and 60mm/s for everything else. BTW, I ramped it up to triple that for a while. Of course acceleration didn't allow it to truly triple but the machine was able to hang in there. The outside surface quality suffered but not as much as I would expect. (I would say that all the surface issues came from the lag from the bowden tube.) Bottomline: go as fast as you want but slow down to 30mm/s for the outside perimeter.