2:2 references the # of wireless radios in the router and the receiving device.
Wireless N is based on an uplink speed of 150Mbps. A single radio router has a theoretical maximum output of 150Mbps (n150). An n300 router has 2 radios and n450 is 3. Wireless adapters are the same. If your router is n300 and your adapter is only n150, then it is 2:1 and no matter how good the router, your speed is limited to the n150 of the adapter. Anything running at an uplink speed of 150Mbps will probably not get you to 50Mbps with any consistency, especially at any kind of distance. 2:2 is an n300 router and an n300 wireless adapter and has the theoretical maximum output of 300Mbps. In reality, they top out at about 80-90Mbps under the best situations and will be creeping down to your stated threshold of 50Mbps by the time the signal has to penetrate some walls and cover some distance.
Errr, no.
Average situations with crummy clients and living situations where you might have a dozen wireless networks near you interfering with yours.
Sure.
In reality under the best situtations, absolutely not. My laptop connecting to my WDR3600, an N600 router, which means 300Mbps 2.4GHz and 300Mbps 5GHz, manages an AVERAGE performance of 185Mbps same room on 2.4GHz and 200Mbps same room on 5GHz. On a 300Mbps connection.
My AC1750 router actually hits 228Mbps with a 2.4GHz 300Mbps connection. That is a 76% yield which is basicly the theoretical maximum you can get, because forward error correction takes up something around 20%. That certainly is NOT a typical connection, it is an awesome router with an awesome client in the same room.
I can get around 190-200Mbps a room over with a wall in the way on 2.4GHz with the same router and client (this is again, 2:2 300Mbps 2.4GHz, NOT 3:3 450Mbps 2.4GHz).
Most clients are crappy clients (like phones), often times with just one radio, interference going on, not close to the router, might be in 20MHz only mode too and so on.
Also, if you want to get technical, the 1:1, 2:2, etc is not the number of radios, it is the number of spatial streams, or radio chains. It is still just one radio per frequency band (unless NON-concurrent dual band, then it is one radio for both bands and it can only speak one frequency band at a time). You could conceivably have, and there ARE, 2:3 and similar routers out there. That means 2 transmitting and 3 receiving spatial streams/radio chains.
Some routers have 3 antennas and 3 receive spatial streams for signal differentiation, but only use 2 antennas and 2 transmit spatial streams for transmitting. That is rare though.