Data rate depends on many factors other than bandwidth (although this is one factor). If the channel is subject to additive noise with a constant power spectral density and with a Gaussian amplitude distribution, then the channel CAPACITY (note: not data rate, which depends on modulation and coding scheme and cannot exceed capacity
if you want error-free communications!) is given by Shannon's Theorem
(capacity = bandwidth * log_2 (1 + S/N),
where S/N is the signal power to noise power ratio. Things are more complex if the channel is subject to more complex noise or interference.
