Plusnet Fibre, Apple Airport Extreme and PS4

[#1]

Hello!
We've just bought a new PS4, which we're connecting via WiFi as the modem / router isn't accessible in the same room.
We're on fibre, so usually 30-50mb speeds on all devices.
On the PS4 we're getting 300kb, maybe 500kb max - so basically unusable, with NAT 2 connection.
We're using an Airport Extreme running in PPPoE plugged in to the modem (not in Bridge Mode)
We've assigned the PS4 a static IP at 10.0.1.201 (with DHCP range 10.0.1.2 - 10.0.1.200), and we've signed up for a static IP from Plusnet.
We've forwarded ports as per guides on portforward.com, and we've got NAT port mapping enabled (although the Airport doesn't support uPnP).
We've tried changing the DNS servers to Google ones, which made a tiny difference but still not above 1mb.
All of this is new to us, as we've no real experience networking but we're trying to move through methodical steps via advice found on the net. Nothing has worked.
So, has anyone got any clue what we could do?

[#2]

A logical first step would be to connect the PS4 and router using an ethernet cable and see if the problem persists.
If this is not possible then a pair of home-plugs could be used.
You could use something like the Wi-Fi analyser app to see if there is a clearer channel available.

[#3]

I wouldn't worry about NAT 2, from what I've read this is OK.  To get NAT 1 I think you need a direct connection with a "real" IP address ie. no router or nat at all.
I don't have a PS4  my self. Some time ago my son phoned with a similar speed issue after getting one. He had started messing around like you. I advised that as all his other kit/consoles were  working it's probably the playstation network being rubbish. He was using home plugs + a BT homehub (which I guess is OK with UPnP unlike yours - so you may need the port forwarding).

[#4]

I had horrendous issues with my PS4, constant drop out on both wireless and Powerline adapters, was also really slow (<1mbps).
I eventually ran a cable up from the router and i'm now getting 6-8Mbps (on a 55Mbps Fibre line!) which is plenty for playing online, takes an age to download anything.
Friend of mine on Sky Broadband gets a better connection to PSN over his 15Mbps ADSL line! It's very frustrating 😞