@rackflot Thanks for the quick reply. Here is my setup. just using the Deco M9 to route wired Ethernet to another computer in my house causes this speed decrease.

I have modified the QOS to be 1024 up and down and removed any favored devices from my configuration.

Why are the wired devices speed downgraded so much? it is only at >25% of the available throughput?

I talked to Xfinity and they indicated the connection was responding with >300mbps speed. Confirmed at PC1. PC2 is throttled. 

Is there any way to fix this? If not, i am going to get rid of these and get the XFinity extender or a different mesh router set.

I have turned off my Xfinity WiFi and am using my Deco WiFi as a Mesh router with the Garage Deco as I thought this would interfere with each other. 

For Wifi configuration, I see that you suggest:

1. Turning on the Xfinity WiFi on the B7.

  @rackflot 

Whoops. I missed a piece of hardware that is causing the problem. The FS605 is a 10/100 mbps unmanaged switch. It appears taht I need a gigabit switch as the switch will negotiate the speed with the B7. After that I will update my cabling to CAT6 from CAT3 or 5, cant remember what i ran but it was a long time ago.

When I am done, I will update this post

I will try the B7 wireless and see if it has the distance I need. Then I will try the Access point suggestion by @David-TP