How do I connect the Box 14 with my Unifi system?

That’s the Speedtest on the cloud gateway. 
didn’t try from pc yet as need to install the 10g switch first, left it on my existing switch for now. 

ips/ids I was looking last night how to check that, also the mtu or clamping, but couldn’t find any of the settings anywhere. 
 

Have ipv6 working too. 

Okay, might be a limitation of the device itself to run such a high speed networktest, try it once you have installed the 10g switch.

About IPS/IDS, you can find it here:

Configuring IDS/IPS
To configure IDS/IPS, follow these steps:

Navigate to Network Settings > Security > Protection.
Toggle on Intrusion Prevention.
Select the networks you wish to apply IPS/IDS to
Configure the Detection Mode as Notify (IDS) or Notify and Block (IPS)
Select the Active Detections you want to apply.

Source

MTU defaults to 1500 on WAN interface, and most likely 1492 on the PPPoE.
We support 1508 on WAN however so you can set a 1500 MTU on the PPPoE.
Don't set a manual MSS Clamping, that should be configured automatically based on the MTU.
Try what works best for you.

Use a MTU size of 1508 on vlan 6 and the WAN port and 1500 on the pppoe interface.

Also check what happens if you turn off IPv6.

What speed do you measure using the V14 (it has an internal Speedtest function as well).

Do you know the server used for the Speedtest on the UCG-Fiber?

I can’t find Mtu settings though, was reading bunch of forums where people can’t see it anymore in the UniFi interface. 
 

v14 box I never tried, didn’t want double NAT and just plugged it straight to the gateway. 
 

had a 3.5gbps Speedtest at 5am this morning but only with 600mb upload. 
just now I see this for a speed test and server:

and these are my protection settings:

I would really check the speed using the V14 just to make sure the bottleneck is not somewhere upstream in the network.

So just for a test, connect the V14 instead of the UCG-Fiber, check the speed and connect the UCG-Fiber again.

Ok will do tonight.

connect to the v14 with its WiFi it creates and in the software gui can run the test?

Yes, there is a Speedtest function in the GUI of the V14.

looks like I get 4 download 3ish up. Not sure what pakket grootte is

When you test the connection on your UCG-Fiber which server is shown during the test?

Netherlands I think?

That is a completely different layout than I expected.

The annoying thing now is that apparently a speedtest is set up to a Ubiquiti server somewhere in the Netherlands (?) and that makes it impossible to compare the measurements on the V12 and the UCG-Fiber. It could be that a route outside of the Network of KPN is the bottleneck

Can you choose a different speedtest server on the UCG-Fiber?

That was from the UniFi app on iOS. 
if it run it from a browser to UniFi console it looks like this

In WiFiman I seem to be able to select these servers, but that’s to run it from my phone not the gateway. But it does mention one of the servers it seems to run on from the gateway. 
 

You got lucky, the fiber has been out of stock for a week. I am waiting to order also haha!

It is very limited, only as the screenshot provided from ​@Andyland.

What I always use for testing is the Oklahoma PC application. It's not an internal modem test, but it's to test the Unifi router speed better and more reliably than the internal Unifi one.

On the internal V14 speed test, I see your upload speed is 2831.
I believe there will soon be an update for your ONT that will resolve this issue (if this is the case for you as well).

The thing is that in order to be able to compare the results you need to use the same speedtest server otherwise you will not be sure to determine the bottleneck.

Edit': In this topic on the Ubiquiti forum I see the topic starter mentions a speed of 4Gbps with a UCG Fiber on XGS-PON from KPN.

This means you should be able to get the full 4Gbps as well.