it all depends on what resolution you plan to run, most cards will be able support 1080p nowadays and Blu ray movies are normally played back at 24 fps anyway so they wont be a challenge to play.
The hobbit was 48 fps but thats still not to bad i used my 560ti to run a 3d movie just fine at 1080p.
The size of the screen wont effect how hard it is to put an image up there. its the resolution thats the demand for the Graphics card, of course larger screens are sometimes needed for higher resolutions, as ive not seen a 1440p res on a monitor smaller than 24".
But for full 1080p HD that Graphics card will be fine