@rhbmcse 

Just thinking, you live in an appartment, usually appartment are not that big, but you are running 4 decos, may this is just to much and the unit are "fighting" to connect to all your devices? I would try to reduce the no. of decos, or allow your devices just to connect to one deco, if those devices are stationary. (for example, the wall mounted TV should onlyx be able to connect to the neares deco...)

Maybe this is all not relevant for your situation, but I experienced switching of devices if decos are to close...

  @Old_Dude 

I'm back to just the two now as I mentioned.  The real question was whether x75s with dedicated 6ghz back haul would alleviate the loss of signal which is congested on the current 5 ghz backhaul band. 

  @rhbmcse it could be , via 6ghz.

but does the issue solve when  connecting only 2 decos ?

  @Decorer247 

No, the speed is still around 300mbps max unless I stand where the main deco is and connect to that, at which point I get 900mbps plus when connected to the main deco rather than the satellite. 

  @rhbmcse

i think you are suffering from , congestion on your location and i think, it might not solve the problem.

also you decos are connected wirelessly which have higher chance of you getting lower speeds as due to interference from other devices speeds are affected.

once you connect each other with wire, things will change else i think whatever the device you buy, you will have this issue.

it is always suggested to put the decos wired.

  @rhbmcse With wireless backhaul, your throughput is affected by the obstacles and the distance between the satellite Deco and the main Deco, as well as by other usage of the wireless bands.

Adding a 6ghz wireless band to the backhaul will perhaps be beneficial, but be aware that this band is more sensitive to obstacles and distance.

You might consider the Deco PX50, with a backhaul combining PowerLine and wireless.

  @rhbmcse 

My 2 cents.

Satellite Deco with WiFi backhaul will provide at most 50% WiFi speed of Main Deco. This is not Deco mesh issue, but limitation of WiFi technology.

If you are getting 400Mbps on Satellite, this is almost 50% of Main Deco speed, which means for dual-band WiFi mesh you are doing quite well.

Switching to tri-band WiFi mesh with 6GHz backhaul should improve Satellite Deco speeds. 6GHz is not congested yet and third band by itself (even if it were 5GHz) will provide an improvement.

Two things to consider when upgrading to Decos with dedicated backhaul band:

1. 6GHz is very sensitive to obstacles, way more than 5GHz. If your two Deco are in direct sight of each other with nothing between them, you should see an improvement. If there is a wall between Main and Satellite Deco, you might not see an improvement at all. With obstacles between Decos you may get better speeds if you switch to 5GHz tri-band Deco with dedicated 5GHz backhaul, such as X68, X90 or X95.

2. Do not expect to see same speeds on Satellite Deco you see on Main Deco, even with dedicated backhaul. I did tests on my tri-band Deco vs dual-band and saw an improvement: speeds of about 60%-70% vs 50% for dual-band. If same valid for you, expect getting 600-700Mbps from Satellite Deco in tri-band mode.

Ask youself if upgrade worth that.

----------------

The only way to have Satellite Deco deliver same speeds as Main Deco is wired connection between them. Ethernet cable might not be an option, but if you have TV cable (coaxial cable) terrminating at Main and at Satellite Deco, it can be repurposed for Ethernet link and I can explain, how.

  @Alexandre. 

This is the most useful response I've had thank you. 

I'm aware of being able to use coax but again, not in the vicinity of either of the decos. 

Ethernet not an option.   I'm stuck with wireless backhaul. 

It is worth it to me to get an extra 10-20%. Thats equivalent to probably 150 mbps. 

I'll take a look at the recommendations and consider. 

Many thanks. 

Rob.