6.5 vs 8 vs 10 woofer


IMHO I think the 8 is the ideal size cone for mid/small sized listening rooms. Even for large size listening rooms. 
The lower mid hz's seem cleaner/clearer. And  there is so little fq's in 905+ of the music we listen to, it seems to me the 8  driver is the most perfect size cone.
A 10 size cone  has the potential to become overwheling, aggressive, attacking when amp gain is pushed just a  tad too much, = Better  volume  control with a  8 vs a 10. 
The 6.5 misses some of that lower bass which a  8 can voice superior. 
After listening to several YT vids with a  10 FR, I had considered going 10, but i think  staying with a  8 avoids regrets. 
I listen at low/mid volume. 

mozartfan
timlub,

That is a pretty nice and concise description of Thiele-Small parameters.  Of course design and implementation are vastly complex matters even when one stays within the proscription of these parameters.  
@larryi    Oh Larry, you are absolutely 100% correct. I was trying to at least give him guidance on where to look for a basic understanding. He would never design anything from that brief description, but it is a start. Recently, I've been playing with how frequency response changes with impedance compensation. Where in the world does that fit in this discussion or how do you get there..... Just 1 step at a time.  I was trying to give him the first step.  
Too many permutations here to have a valid discussion. For example, a bi-amped system with electronic XOs allows for a dedicated amp to control the bass driver and not need as much passive XO at the speaker level. 
Then there is amp design, driver quality, damping factor and slew rates, etc. 
Douglas what would you buy?  Are you a dealer. I think this discussion makes sense because a lot of us are confused on this subject.

I thought he was basically asking a question rather than trying to tell us what is best.

I think we would like to hear what you have to say.  This is a question many of us have.  This also depends on whether you are using a pair of subs to fill in the lower frequencies.