having just been all around the Wifi/router/powerline adaptor/ethernet cable domestic network setup I can add a little info here.
The incoming data stream to our home manages 37Mbs, this I have proved using a broadband speed checker. It measures both download and upload speeds. If I connect a laptop to the modem/router by ethernet cable I get the 37Mbs. If I link to it wirelessly I get 37Mbs but only when the laptop is close to the modem/router. Go into the next room and it soon starts to slow down. If I use a pair of powerline adaptors (push the data steam through the mains wiring) I get 12Mbs in most rooms in the house but it doesn't work out to my workshop in an outbuilding.
The laptop has both 2.4Ghz and 5GHz available.
On my netbook things are a little worse as it only has 2.4GHz available and we have a number of conflicting signals from neighbours overlapping our channels on 2.4GHz. As a rule of thumb, the signal to my fastest machine, running Linus Mint, as reported by it's network driver, is only 68-70% (don't know if that is a quality or signal strength figure) and the link delivers a consistent 20Mbs between the back bedroom window and the out building workshop.
If you get signal conflicts from neighbours equipment speed falls off very quickly. On my netbook I have a freeby (may be not free anymore) called Inssider that uses the wifi and or GPS hardware in a PC to monitor and display local signal conditions. You can easily see what channels are in use and then log into your own router and move it to a channel which gives less conflict.
Andrew.