I've read how the 4T will offer superior mids, be easier to power, are able to produce lower frequencies, and will offer more sound. Also that the difference is most significant for music. I generally listen to music in 5 channel stereo, a little multi channel, and never strictly 2 channel. I have 5Bs for fronts right now, 5C & 4Bs. In the near future I will be upgrading my sub to the 8D so taking that into consideration how significant will the difference be if I upgrade my 5Bs to 4Ts?

From what I have found most people say with a good sub the difference between towers & bookshelves is negligible but I didn't want to go off of generalizations. If it matters my listening area is about 12'x10'. I'll also be upgrading my receiver to a mid-level onkyo most likely, and live in an apartment, so power/volume aren't really a concern.

 Thanks.