This is just in generic 4:3. If you are using a 1080p TV then 4x in PAL is actually 1152p which is more than 1080p already, meaning you don’t even need 5x. What you want to do is set it to 4x and make sure 4x is set to generic 4:3, then just go to sampling options and at advanced timing just press ok on the one that’s there as that’s the one that’s corrently in use, then set those options I mentioned and see if you get a picture.
EDIT: My mistake, I just seen that you have a 4K set. You’re getting the same vertical resolution in 4x with the settings I have mentioned (1080p) and for 5x PAL, you’re going up to 1340p meaning that 1200 is still going to be missing some detail vertically. I guess it is a bit of a shame but 4x with those settings should look amazing on your TV. I can only get 3x on my Panasonic 4k set in NTSC and can only get 2x PAL 16:9 stretched, so you’re doing much better than me 🙂