I recommend testing the PS4 WiFi connection speed at about 10ft distance from the router if you can.
What are the speed results on the PS4 when hard wired to the router?
Do other wireless devices exhibit this same speed result?
One other thought I had, knowing that some mfr of game consoles install WiFi adapters and are tailored to be somewhat held to WiFi standards, however going forward, there maybe some drivers with in these game consoles that may not be quiet standardized thus maybe introducing some problems between the WiFi adapter on the console and the main host routers WiFi. We've seen this before on Xbox 360 Slims.
One thing you could do as a test if you can get one, get either a 2.4Ghz or 5Ghz Wireless bridge and connect it to the 5500. Shut OFF the Wifi on the game console and hard wire the PS4 to the bridge and run some tests...This should have 2 results, good or the same I believe...