It looks about the same to me, just as good as my 4XL.
Looking and playing with both the 6 and 6 Pro at Verizon last week, I honestly could not see a differences between a 6 and the 4XL. But honestly did not run any videos, other than the animations on the phones for display at the store. However, comparing the larger 6P, it was noticeably nicer than even my 4XL.
I have a 4XL and admittedly it is a fantastic screen, and has been an excellent phone.
My suggestion is if you can find one to view at a store. My eyes are probably older than yours.