It all depends on the movies you purchase. if the 4k movies you buy are truly 4k(lucy, xmen apocalypse, batman vs. superman, etc) then the picture difference will be superior however if the 4k disc you purchase are not truly 4k movies(suicide squad, secret life of pets, ghostbusters, etc) and just upscales you might as well just stick with regular blurry\
also be sure you have a 4k tv
heres a list of real and fake 4k movies
http://realorfake4k.com/list/