@Daniel9789 

> How do I now measure the current speed on the main Deco?

It is not as convenient as with M5, but if you have desktop or laptop with gigabit Ethernet card wired to your home network, you can run speed test app on it and that should give you same result as speedtest in Deco M5.

> 2) The main X60 is plugged into the router and then the same X60 also plugs into a Ethernet gigabyte hub.

Yes, this is OK. You screenshot shows Satellite X60 connected with Ethernet, meaning everything is fine.

> speed test of one device on that Deco was 900gb and another only 500gb - maybe its the wiring, maybe the second device just isn't as good).

Maybe. As long as you can get 900Mbps on at least one device, it means your Deco delivers these speeds.

>Security settings. Which should I pick? WPA, WPA2, WPA3 etc? What's the difference?

Bigger number - better security for device to Deco connection (newer and improved security protocol). Start with WPA3, if you find wireless device that refuses to connect, downgrade to WPA2. They all should connect at that point. Using just WPA is not recommended.

>I've got devices sat beside the main Deco that want to connect to the Deco in the house furthest away and vice versa. Would it improve the network if I choose a preferred Deco for then to connect to so they aren't connecting far away, or does this actually give a negative effect overall?

Purist would say that binding device to WiFi mesh unit goes against the spirit and idea of WiFi mesh. In true WiFi mesh its nodes (Decos) and wireless devices decide on their own where to connect. 

Realist like me would say the following: if device is stationary, such as Smart TV or desktop and it connects not to the nearest Deco and its WiFi speeds are not satisfactory - use preferred Deco connection to tune it.

In all other cases - just let it be. 

> IPv6 - what is it? Should i turn it on or leave it off?

You can turn it off. No need for that in home network. No harm to keep it on either. 

>speed is levelling out around the 900gb mark and not the 1150 mark thats advertised

Your ISP might promise and deliver fast speeds, but your home network is limited by gigabit switches and gigabit Deco Ethernet ports, which in reality means up to 940Mbps in speed tests. What you have is excellent speed. 

  @Alexandre. 
 

Thank you for the comprehensive reply.

If I could elaborate on some of my Qs and your Answers please and thank you?

1) Understood. I have nothing plugged into Deco 1 that's PC based so can't test, but Deco 2 is hard wired to Deco 1 via a gigabit hub and that speed tests 900gb. I just wondered if I'd lost speed due to both the hub and the second Deco and whether Deco 1 would be outputting higher.

2) Also understood. Very much can't understand why one device is 900 and another 200-500, but it must be a device limitation as the deco clearly puts out enough to give device 1 the 900.

3) security understood thank you.

4) Most of the devices are stationary. They also aren't devices I can speed check/test as they aren't pc based so can't run a speed test, but they are things like CCTV which seem a bit oddly picked up by the nodes.

5) I've got IPv6 turned on via the TP link app, I'll turn it back off.

Regarding hubs and speed. My new Virgin Media Hub 5 has a port that's capable of outputting 2.5gb, I'm not utilising that if course as my gigabit hubs max out at that gb. Is there a hub in existence that increases the speed beyond the 1gig to utilise the 2.5 port the Virgin router outputs? I appreciate my internet is only 1.15gb and not 2.5, but as tech increases it's worth having, and I can squeeze that extra couple of hundred mb out of my system at the same time.

Lastly I'm seeing on the TP link website the firmware of mine is V3. There is a V3.2 but no firmware attached. Is this a new model, or a BETA or something?

  @Daniel9789 

For speed tests on gigabit home network, having 900Mbps is good result. You are not losing speeds - your Decos also have gigabit Ethernet ports. In theory it is 1024Mbps, in practice is not. 

I missed CCTV devices when discussed preferred connection. For devices that generate data stream, such as CCTV cameras, you should set preferred connection. In comparison, for little data traffic devices such as Smart thermostat or Smart plug setting preferred connection is unnecessary.

In many cases, WiFi code in such devices is quite old and have not been updated for a while. Meaning, when code was written programmer may not even considered WiFi mesh. That code might randomly find first Deco node with proper SSID/password and just connect to it. That is especially true for devices that only run on WiFi 2.4GHz and do not support WiFi5. That alone says their WiFi code may not have been updated since times when most households had single WiFi router.

There are Deco units that support 2.5Gbps Ethernet. If you want one of those, check Deco X90, X95 and XE75 Pro. You may find them much pricier that X60s. To get benefit from 2.5Gbps port, use one of those as Main Deco and connect its 2.5Gbps port to Virgin Hub.

>Lastly I'm seeing on the TP link website the firmware of mine is V3. There is a V3.2 but no firmware attached. 

TP-Link is known to release different hardware versions of same device model, and sometimes that hardware results in having firmware with different options, even for same model. For example, if I am not mistaken X60 V1 supports speed test feature M5 has. Yours X60 V3 does not.

Just use "Update Deco" button in Deco app and when TP-Link publishes new firmware that is for your Deco X60 hardware, it will be correctly installed through the app.

  @Alexandre. 
 

Thank you again.

Annoyingly it seems like my M5 Deco I could manually tell each device where to connect, yet in the X60s I cannot. They connect where they like and not where I want. Hopefully they resolve that ASAP.

I think given the cost and the internet speed, the X95 or XE75 pro is probably futile at this point. I'm getting 1gb (or close too, so probably should be satisfied with that).

Understood on firmware, I'll remain in the app and only update when told.

  @Daniel9789 

About connection preference - sorry, missed the fact X60 does not support it yet. I doubt we will see its firmware upgraded soon to have that feature: TP-Link haven't released even beta firmware with that feature for X60 yet.

Deco X50 and X55, which are similar to X60, have firmware with connection preference feature. If you can exchange your X60 set for X50/X55 set, you'll get back features you had in Deco M5. Except, perhaps, Deco app speed test - not sure about that.