I wouldn't buy a 4k laptop for gaming. Since the native resolution is 4k, that's what you'll want to play games at. Considering the best desktop graphics cards can struggle with 60fps on newer games at 4k, a laptops gpu performance at 4k will suffer a lot without a lot of compromising. Of course it's personal preference what someone considers playable (30/60fps, low/high settings, etc.). I'm not sure about the "even if played at 1080p" comment. The games won't look as good@1080p, but you will benefit from increased performance as the system isn't being taxed as much, regardless if the native resolution is 4k. One thing to mention though is a 4k screen takes a lot more juice to power so the battery life most likely will be in the toilet compared to a 1080p model, and if you plan to game on the go, that'll put a hurtin' on play time.
EDIT: Geez, start typing with zero replies and find a ton by the time I'm done, lol.