A:Answer That is not an easy question to answer. The best i can tell you is that the 5g is able to penetrate walls and ceilings, but the 2.4g penetrates much better. It might be good to do a dual band router so you have the option of switching in case your 5g band gets slow.
You could use a second router with exact same wifi settings, some people do that instead of an extender. There is also ASUS 1900 package that comes with an extender, and I think they sell it separately for $60.
Usually people are stuck with the location, they tend to have it next to the cable modem. The nighthawk seems to have good range in my large 3 story house.
