Discussed at length in the thread archives.
The answer is 200 watts.
Because distortion from tube amps is perceived more favorably by the human ear than distortion from solid state amps, a lower power tube amp may *appear* to work as well as a higher powered solid state amp simply because the listener is not as bothered by the tube amp's early distortion as it reaches clipping.
Nevertheless, 200 watts is 200 watts, and if the speaker manufacturer recommends 200 watts, then that's what you should feed it at minimum, regardless of whether the amp is tube or solid state.
IMO.
