@Aidy2020 

With M9 Plus and gigabit Internet link, expect WiFi speed on Main Deco to be up to 500-600Mbps if everything is right. M9 Plus is WiFi5. It can't deliver gigabit speeds, so you need to decide if you want to spend time troubleshooting your Deco mesh, with end result of about what you had before, or perhaps it is time to upgrade to WiFi6/6E/7 capable mesh.

Virgin hub5 supports WiFi6, which means it can deliver faster WiFi speeds than M9 Plus Main Deco. If you place smartphone very close to hub5 and run speed tests on it, you may see speeds reaching gigabit, which is speed of your Internet link.

@Alexandre. Thank you for your reply.

What would you recommend to replace the M9 Plus's with?

It's just strange because I am getting worse speeds now that I've upgraded, compto what I was before and nothing has changed apart from my router and fibre speeds.

  @Aidy2020 

I can't explain why are you getting worse speeds, especially why in Access Point mode. I have Deco mesh with M9 Plus, I went through ISP router replacement with no issues.

Just connecting Main Deco to a different ISP router should not degrade Deco mesh speeds. Perhaps, something else changed at your house or at neighbours that impacts WiFi signal and it coincided with you switching to hub5.

As I said, the best you could get is speeds you had before, M9 Plus can't provide gigabit speeds. 

Basic troubleshooting that I would recommend:

1. With Deco mesh in Router mode, run "Test Internet Speed" from Deco app and see if you are getting close to gigabit speeds. This will test wired link from Main Deco to hub5 and to Internet.

2. Up QoS parameter values to 800/800: How to set up QoS on the Deco

3. Run Network Optimization in Deco app and check speeds after that

4. Turn off hub5 WiFi - maybe its strong signal creates interference with Deco mesh. 

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Your hub5 seem to be quite capable. From your own words, before you had 250Mbps on top floor with Satellite Deco, now you have 200Mbps from hub5 alone. Maybe you can just power off Deco mesh and run your house WiFi off the hub 5.

Also, check with Virgin if they can provide you with WiFi pods compatible with hub 5: you may be able to get them for free. This is what I have found: "If you’re a Virgin Media customer with Gigabit Fibre Broadband, you can get up to three signal-boosting WiFi Pods (if needed) at no extra." 

They don't allow external links here, this is taken from Virgin Media/Help/How-to section, article named "How to get Virgin Media WiFi Pods."

I would recommend to replace Deco mesh with hub5 pod(s), as a start. If they do work for you, no need to look for anything else.