I have not tried on the treksport, but you are right, the models have different sizing. For example, the speeds I have tried have been as if M40 is the same as W40. The spyridos in m40 were tooooooo big withwise so I could not buy them. The bikilas I have tried in M40 have been just fine. So, the models do vary.
The white are sized up to W42, but you can use them in 41 or 42, that is deppending on how high arched or fat toed you are; they are just like the bilkilas, and if you have narrow feet, then there would be no problem at all, speeds are "the" model.
It depends, are your feet bulkie or with high instep? When I tried on the spyridon ls, they were too wise and felt big, being my size; alsom not all models feel the same and, if they are your first pair, vibrams do not feel the same as non toed shoes.