Those tests don't make much sense to me. Are the 6700K and the 2500K both running at 4.5Ghz? I don't see a clockspeed listed for the 2500K, only the 6700K -- That means either both are running at 4.5Ghz or the 6700K is overclocked and the 2500K is running stock, which is a huge disadvantage for the older chip.
Also, in the only GPU limited game in the test, Rise of the Tomb Raider, both chips performed equally. Anno 2205, SW:Battlefront, and XCOM2 are all CPU dependent games (SW:Battlefront is CPU limited because of the high framerate).
In most cases the 2500K @ 4.5Ghz is not going to limit you if you're running 1440P with a GTX980TI, as the card will struggle enough on its own to hold a steady 60+ FPS. At 1080P you may be slightly limited, but I don't suspect by much, except in the games listed above as well as Total War, etc.