Graphics cards for big display monitors

I have never seen a 50 inch display monitor, although it is a fairly common size for HDTV. The number of pixels does increase the effective area of display. So if you have an image that occupies 100 x 100 pixels you will be able to fit more of them on a screen with a higher resolution. You will not be able to fit any more of them in a bigger screen with the same resolution. Specifically on a 1920 x 1080 = 2,073,600 total pixels monitor you could fit 207 such images on the screen, on a  3840 x 2160 = 8,294,400 pixels you can fit 829 of them. So roughly four times as much space to display the images. The visible size of the displayed images at the screen will depend on the geometry of the screen, but if you have the height and width you can calculate the dimensions. The effective size will depend as well on how far away you will be sitting.
 
The problem with that big a monitor would be placing it far enough away for comfortable viewing. With more pixels you will not be seeing discreet dots sitting at an equal distance as with a lower number of pixels per square inch, but I expect a screen that big at the distance you are used to viewing from might be pretty overwhelming. You should probably try one out in a store to see if it makes sense, and try to imagine staring at it for hours.
 
As far as a video card, it has to have outputs that match at least one of the inputs of your monitor, a digital connection is a good idea, and it should  be able to deliver the native resolution of the monitor. If all you are going to use it for is Sonar, then response time is not very important, nor is color gamut etc. If you are gaming or planning on viewing videos that is a different story.

i think all you need is a high def tv with hmdi input, and a hmdi output on the pc