@arunsethu thank you. here are the test results

• existing setup: (Hub 4 on modem mode, M5 serving as router) -  over wifi on iphone, speedtest.net result - 204 Mbps download, 46 Mbps upload; speedtest on Deco app - 667, 52
• existing setup:  used Deco cable to connect laptop to M5 and checked speedest on laptop - 435, 52
• used deco cable to connect M5 to hub4, speed test on laptop over wifi - 389,51
• used deco cable to connect M5 to hub4, speed test on iphone over wifi - 415,50
• used deco cable to connect M5 to hub4, deco app spped test on iphone over wifi - 666,52

As you mentioned, I also tried to connect my laptop directly to the port on Hub4 that served Deco M5, however I couldnt test as its no internet as the Hub was in modem mode.

As you can see from above, I hardly get more than 400-500 Mbps over wifi/ethernt and the Deco app speed test doesnt go beyond 600 Mbps. 

Please advise if there is anything else you want me to try before I reach out to Virgin

@arunsethu 

I don't think of anything else you can do, except changing back hub4 to gateway (modem and router) mode, disconnecting everything from it wired and wireless, connecting laptop to it by Ethernet cable and running speedtest. 

You need as simple speed test as possible, so that Virgin support won't dismiss your escalation as "third party hardware issues." 

Alternatively, if you are fine with speed you are currently getting, I would suggest just downgrading your Internet package to 500Mbps or anything available from your ISP in the range of 400Mbps-600Mbps. Saves money and aggravation of taking to tech support.

For regular household 500Mbps is more than enough, it is equivalent of streaming 4K content on more than 10 devices (TVs, tablets, set-top boxes, etc) simultaneously.

Besides, even in an ideal configuration, you won't get more than 850Mbps over WiFi on 5GHz and 300-400Mbps on 2.4GHz, with M5 and E4 Deco hardware. 1 gigabit ISP speed is an overkill for Deco mesh you are running.

@Alexandre. thanks and sorry for the late response. I am trying to talk to the Virgin customer support which is non-existent. was on the line for more than 2.5 hours yesterday and gave up finally. Will try again this week. I did test the speed buy switching to Router mode and making sure I am the only device connected. Still dont get more than 400-450 Mbps on my laptop both on samknows/realspeed and on Speedtest site. Not sure whats going wrong where.

On Deco I understand there is a limitation on the speed, if I was getting 800+ speed I wouldn't complain.but am not getting more than 200-300 on WiFi even on a good day which is ridiculous. Anyway will update once I hear back from Virgin support.

@arunsethu 

 I get full speed 900mb from tp link deco via ethernet.

However when I test with one main deco via WiFi I still get 200mb on all WiFi devices.

https://community.tp-link.com/en/home/forum/topic/249988

@arunsethu 

 I get full speed 900mb from tp link deco via ethernet.

However when I test with one main deco via WiFi I still get 200mb on all WiFi devices.

Any advice?