I've gone for 40mm x 40mm aluminium profile for the bed on my machine currently under construction. I considered 160mm x 16mm and 160mm x 28mm but thought it would not be stiff enough. I'd have thought a 10mm or even 20mm solid sheet would be rather flexible over large areas too, do you support it a lot?

I guess I'll still need a sacrificial bed on top of that, and I'm not sure what to do since that will stop me being able to easily clamp stuff down on the profile.