Also worth checking that the laptop is definitely using the 5GHZ band and not the 2.4, if it can't get a good signal on 5 it'll drop to the 2.4 as backup, my phone has a habit of doing this if I wander out of 5 GHZ range and then doesn't always revert to 5GHZ when I come back in again. Settings>network status>properties button and scroll down should tell you what it's doing (and the link speed, which isn't the speed of the internet connection, just the one between laptop and router).