Hey Magma
Firstly let me comment on the strength/warp factor of plexiglass. I agree that it hardly bends/flexes with a 60 kg load but do consider that your man is not going to stand there for long but your eqpt surely will be there for periods long enough to induce discernible flex. Also, i do not completely agree with venkatcr that a reasonably thick acrylic sheet will snap easily by tightening. For that one has to be very stupid or very strong, maybe both. They use this stuff to make dance floors in nightclubs for people to hop n jump upon.
Magma, I do agree with the factors that you have listed but then being far from any kind of GuruI daresay both my racks were done by a seasoned machinist with minimum machining tolerance gaps. Its not zero but almost as good or else the rods wont enter the holes. Ather reason for sway is the use of spikes as this drastically reduces the surface area of ground contact to a single POINT. Hence SS floorpads become mandatory. Even better if you place the four floorpads on a thick and rigid rug(not the fluffy sort), then mount your rack on that. That way, not only can you pull the rug back n forth easily on a polished/tiled floor (to reach the rear of the rack to change connections) but it protects your precious floor from stains/marks over prolonged periods. With load on your rack, the pads get embedded into the rug creating a slot for themselves forever so make sure you dont try this with the wife's favourite persian carpet. You ll see what I mean when you see the snaps of my friends setup n Guwahati. For my rack, which is about one half bigger, I am using a 3/4" plywood piece as a base(the floorpads are placed on the board) to move the rack for making/ changing connections the rear. More later