4k UHD is amazing and an experience. You can stream losslessy from plex if your client supports the audio and video formats. Also, if you have an older blu-ray player on your PC it might already support UHD. Without buying any new equipment, I was able to stream Planet Earth 2 from Plex to my 4k tvs. I picked up Planet Earth 2/blue planet 2 UHD combo on black Friday for like $20.
Worth every penny.