i used 25mm profiles... they sit nicley over the aluminium profile slots and i though id sooner go over the top and play it safe but looking back now i think could have made my machine half the weight and had it perform pretty much the same as it does

iv even used 20mm rails on my Z

its only a small machine, aprox 350mm x 500mm cutting aria... i would need to strip it down to move it :(

i doubt you have missed anything jonathan, i think people play it safe when buying profile rails... they tend to be exspensive no matter what size they are