Poor Wifi signal and speeds with NightHawk XR500 and EX8000.

I have a 3,400 sq ft poured concrete home. The majority of living space is on the main floor, which is open concept. That's also where the extender is located on the west end of the house. The upstairs spare bedroom and separate livingroom is where the internet comes into the house and is where the router is connected at the east end of the house. The internet "speed" we pay for is up to 200Mbps from cable. The cable company says it's coming into the house at close to the speeds we're supposed to get. I've called Netgear Support numerous times about the speeds and we can't seem to get it figured out. My desktop is lucky to get 40 Mbps, laptop gets about 20 and my phone gets over 100 download. All connected to the same network. After the numerous resets and settings changes that we've done over the last month I was wondering that being the concrete walls and upper concrete floor if I should get another extender or is it actually something in the settings of the router. Thanks in advance for any input.