Nah, the upscaling is so good on the newer models that if it's proper 1080p content it will still look great. Low bitrate 1080p content won't, but that's the same even on a 55 incher!
A guide to the best viewing distances when watching Full HD or Ultra HD 4K TVs.
www.avforums.com
suggests at that distance a UHD screen is only just going to be worth having?
1.6 x the diagonal (77 inches) is generally the 'optimum' TV viewing distance = 123.2 inches or 10 feet 3.2 inches... so move a little closer if you can