People tend to pick the size of their flat TV based on the amount of space they have for it, this isn't necessarily wise. Flat TVs take up much less space than you might think, so your new TV may end up a foot or two further away from your viewing position, making the picture appear smaller.
Also, with hi-def, you can have a bigger screen and the same viewing distance without worrying about seeing blemishes inherent to the source. A 4K TV's lack of noise means that the ideal distance to sit from the screen is three to four times the height of the TV.