Alienware 17 R4 UHD VS Alienware 17 R4 WQHD same specs weird stuff

So I did own the Alienware 17 r4 UHD 4k Display with 7700hq and Nvidia 1070, so I broke it and so my parents paid for me to buy a new one off ebay and so I bought the Alienware 17 r4 WITH THE SAME SPECS just this version has a 120hz display and 2k 1440p

however umm.... something really different about the 2, the 4k version LAGGED BADLY on high to ultra settings however this version my WQHD 120hz version plays everything on max setting without ANY lag whatsoever im thinking over time because my new AW17 was lightly used when I ordered it off ebay and sure enough it still had the clear wrap on it, and it was BRAND NEW so my point is is over time the system corrupts itself or something go's out that makes it become laggy anyone else suspect age = lag