They do fit big I have some L SMS Mrider pants and I'm 6'2".
They fit me with low-medium bag, if you want something pretty baggy go with L, if you want something less than that im sure M would still work for you.
i just got some m rider pants and there a large and im only 5 9, and they fit fine. the waist on them has velcro straps so you can do em up tight around the waist and keep em up. the only real difference between the medium and large is and inch or two in the waist and a few inches longer in the leg, the leg width hardly differs.