I'm pretty much convinced that I should switch to profile rails instead. I guess 15mm should be enough?
Something along the lines of: http://www.aliexpress.com/item/China...489001007.html or http://www.aliexpress.com/item/6-x-H...934543282.html

What should I consider when switching to square rail? Can I mount the rail straight to the extrusion t-slot? Any special considerations?