I am not sure the vox coat is Steed, though I'm not sure it's not either, but I think it is not. I know the slewfoot suit is Steed,
In any event, the key difference is that slew has a lot more obvious drape or excess chest. Vox's coat is leaner and more "parenthetical" in silhouette. What you see david wearing there is much more representative of what steed makes for most people, including me.