Just read it for the third time and don't see where the OP asked for "bass". I must be looking at a different version of this thread than you.
A 2 way 6" x 9" can reproduce a wider frequency range than a 2 way 6.5" because it has a larger cone, therefore can move more air, therefore can reproduce lower frequencies, all things being the same. There's a reason we use larger drivers to reproduce lower frequencies. If you're under the assumption that a smaller cone is capable of reproducing a lower range of frequencies than a larger cone, then please, enlighten us as to the physics behind your theory.
As a side note, usje, take the manufacturers rated frequency response statements with a grain of salt. There is no market standard imposed for their ratings, and aside from figures such as sensitivity (usually rated when driven at a certain frequency with one watt at one meter), each manufacturer is free to test them as they see fit. It's (usually) fine to compare the same manufacturer's specs among their own products, but they can and do deviate greatly from manufacturer to manufacturer due not only to design but due to different methods of testing.
Each speaker will also perform differently depending on what it's mounted in and what is around it. Some speakers sound better when on-axis, but sound terrible off-axis. Others have very wide dispersion patterns but give up sensitivity to achieve this.
