It is not so much the noise floor as it is the difference between the noise floor and the received signal - this is called Signal-to-Noise ( S/N ) ratio. What you are looking for is about 20db or more between the noise floor and the received signal, i.e.,
received signal = -65db, noise floor= -90db, S/N = 25db, this is good.
received signal = -85db, noise floor= -90db, S/N = 5db, this is not good....
thom.lawless [at] rapidwifi.com