Personally I have no experience with any of these laptops, I'm only informed by reviews, and I am going to be owning the msi gs70 stealth in about 2 weeks. In my opinion 720p is plenty fine with me. I'm not much of a fan of these 3k or 4k displays. I play to game, not to make my displays all pretty. Though if i had an opportunity to own a 3k or 4k display, sure I would take it.
If you have the money to spend, I would personally enjoy using the msi gs60 3k display, but I would end up hooking it to a monitor anyways, so the 3k would kind of be pointless for me lol.
As for the Asus gx500, it maybe 4k but you still only have a 860m according to asus's website, as for the msi gs60 it comes with 870m.
Here is a comparison of the two GPUs. The asus gx500 states no HDD space or RAM, so who knows what you will get. For a 4k display, im going to guess the price be around $2,600. I doubt that this laptop will be anything specially, I'm pretty sure they are just getting a thin high performance laptop on the market to compete with msi, Razer, and who ever else has a thin high performance laptop.
Oh yeah, Razer's laptops are nice, but they are overpriced, so be weary of that.