Hello -
Your question is quite a complex one. On theory it is bounded by Shannon's Theorem:
http://en.m.wikipedia.org/wiki/Shannon–Hartley_theorem
The question you ask in practice is actually not limited by the USRP or its bandwidth, but the amount of host processing required. The Rx side is almost always the most resource intensive due to the computational effort needed for matching a symboll rate snd impairment correction such as fractional resampling, frequency offset correction, and error correction decoding convolutional codes.
The maximum Tx bandwidth is 40MHz in 8 bit mode and works in short bursts or recorded to (high rate) hard drives. The Maximum data rate of decoded communication is probably in the low single digits of Mb/sec due to processing overhead.
