I'm considering preordering either Vue 6 xStream  or Vue 6 Infinite.  
Vue 6 xStream enables Vue 6 scenes exported to Maya, 3DSMax, Lightwave and Cinema 4D and render scenes in these higher end 3D applications.
I'll invest in C4D in the near future (for modeling purpose), too. 

1. But how much better is the render engine of Cinema4D than Vue 6 Infinite's?
   If C4D's render engine is not significantly better and faster than Vue 6's, I will buy Vue 6 Infinite and import scenes/models from C4D and render in V6I instead.

2. According to the official e-on Web site, the download file of  Vue 6 xStream is 820MB in size, while Vue 6 Infinite is 890MB.   Why is it such difference?   Shouldn't the xStream file be larger than Infinite, since it's suppose to have more function/features?

Your inputs are much appreciated!

The Vue items imported into the other app using Extream will still render with the Vue render engin - you will not get any speed improvements.  It only allows things like eco-systems to be brought into the other app.  In my mind, it's a much better to bring in the models into Vue and render eveything in Vue. 

If you intend to use Cinema for modelling ONLY, you don't need xStream. If you intend to build scenes in Cinema and add Vue atmospheres, ecosystems, terrains, etc, then you need xStream.
Xstream doesn't have more functions/features than Vue Infinite, basically xStream  IS Infinite, but it is Vue Infinite right inside Cinema4D, without the need to import/export, go back to Vue to change settings, re-export to Cinema, etc, etc.
Also consider that ecosystems don't export to any other app.
Cinema 4D's advanced renderer is the fastest around, but the Vue elements will be rendered by the Vue renderer, even within Cinema4d, with Vue 6 xStream, as Peggy said.

I would agree to my "fore-writers" here... Do all the modelling in Cinema, Rhino whatever - import it all to Vue and render there. This works excellent for me because Vue is very good in importing several formats (including native Poser import etc.).

Hold on I want to make sure that I understand this.  So if I create a scene in Cinema 4d and it uses Vue trees, but render the scene in Cinema 4d with the toon shader, everything will be toon shaded, except the trees?  That does not sound good to me.

Maybe I'm missing something...

David

Vue materials are applied to Vue objects, C4D materials are applied to C4D objects, so Vue trees wouldn't be cell shaded. 
What you get with the xStream plug in is correct lighting on all elements based on the Vue atmosphere, Vue elements reflecting C4 elements and vice versa, Vue elements shadowing C4D elements and vice versa, C4D objects projecting shadows according to the Vue sun.
If you want cell shaded Vue trees, you need to export them form Vue6, import them in C4D and apply C4D materials to this new object.
I suggest you read what exactly Vue xStream is at e-on's site.

Hi there. Thanks for your reply. I will take a closer look at the website. David

Thank you all for the inputs!
Ashley

I also am considering Vue6 xtreme to integrate into C4D - because I thought that it would render it with the C4D renderer which is lightning fast (in my opinion)

So what you're saying, is that it will render all vue bits in the frame at Vue rate and all other parts at C4D rate?  Will that not still be faster than ALL rendered at Vue rate?