C4D is one of the fastest renderers around, the comparison is tough, and Vue can't win. Vue isn't fast, but there are many options to speed up render times. What atmosphere were you using? If the default spectral atmo, you can't compare it to a C4D sky. plus, this atmo is set to global ambience, which is the fastest " GI" solution with Vue, but an advanced lighting model nonetheless. You can lower the atmo quality down to -1 without any artifacts, and it will  render almost twice as fast.
Now about xStream, C4D elements are rendered by C4D, and Vue elements are rendered by Vue so there is no speed difference.