A lot depends on what app you would use to view the videos. I recommend you get Plex and set up the Plex server on the Shield. You can use the RPi as a file server and have the Shield access that. The RPi will get plenty of "mbps" for you... I do recommend you use a wired connection.

For torrenting, this is the wrong sub to ask about. IIRC there is a torrenting sub out there that may help.