6.5 vs 8 vs 10 woofer

@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.

I am listening to right now, a 15 that is 95db sensitivity, but only goes down to 38hz

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I would have figured a  15 goes BELOW 20hz.. Ok so the inner core also makes a  huge dif on how low a  8 inch will go.

Look Vox/USA just reached out, So Vox is back on the table.
And thinking things over,,although I figured a 10 will go into the low 30hz's, and the 8 low 40's, might not hold water. 
The 10 perhaps will go lower, however I've been living with dual 6/5's and have missed the lower bass for now 20 years, A 8 super high 98 sens will deliver the clean tight low, say maybe low30's, and thats allright with me. The Vox 8 looks to be ~~meticulously  hand crafted~~ and this may result in a  finer resolution of 100hz-say 1500 hz;s where most of my classical music falls. 
So it looks like the Vox 8 will be the next step in this FR/High sens journey, which is all completely new to me.
Just got word from the Vox /USA dealer, he has employed all sorts of PP tubes with Vox and has nothing to complain about.
So ~~Ideally SET  ~The Perfect Match~~, Due to finances (Defy upgrades well over $1k)  SET is off the table.
Now I have to go ck my topic over on amps, see if anyone has a few ideas how i can tweak,  the Defy to better match a  high sens speaker.
See you guys over there.

larry5729, I am a reviewer for Dagogo.com, online magazine for 14 years. If you wish to see the speakers I have written up over that period, you can click on the "Staff" tab and look at my articles. BTW, "staff" is a bit of a misnomer, as I have not been paid to write. I push myself to do deep, involved articles for the love of the hobby, art, and personal advantage in development of methods that will allow me to achieve better systems.

With that background, I have used all manner of speakers in regards to bass; concentric/full range (i.e. Tannoy Glenair), horn hybrid (i.e. PureAudioProject Trio15 Horn1; disclaimer, I am currently reviewing another PAP speaker), dynamic (i.e. the Salk Sound SS 9.5 Speaker review just published), hybrid dynamic (i.e. a favorite, the Vapor Audio Nimbus White), dynamic hybrid array (Legacy Audio Whisper DSW Clarity Edition), Magnetic Planar (owned Maggie 1.6 QR, and reviewed hybrid magnetic planar Eminent Tech LFT-8A/B), ESL hybrid (own King Sound Guitar speaker, full range ESL (Sound Lab Ultimate 545), ESL array (Kingsound King I and III reviewed, and I own the King III), Open Baffle (Tri-Art-Art Audio B Series 5 Open), Transmission Line (Van L Speakerworks Silhouette), Dynamic hybrid with integral subwoofer (Legacy Audio V and Valor Speaker Systems), various bookshelf speakers too numerous owned or reviewed to mention; the Lenehan ML1 Reference was delightful), Quasi-D’Appolito (Daedalus Audio Ulysses), Line Source (Raven Design Studio Ebb), Omnidirectional (King Sound King Tower, and Ohm Acoustics Walsh Model F. I think the list covers most genres of bass technology that I have heard in my room.

I have used from a single 5-6" woofer, to sets from two to twelve 15" woofers. I have used many bookshelf speakers over 30 years with and without active subs. I also have used many towers with active subs, and some, like the Daedalus, with matching passive subs.

Every one is distinct and has unique characteristics. So, I find it horridly opinionated for an individual who is gleaning info from YT to be declarative in attempting to tell the community which bass genre/technology is best.

My favorites? None, if not set up well. Several, if set up well.
Over the years I am moving away from standard dynamic speaker towers. I am moving increasingly toward Open Baffle and Dipole (with or without subs). I can hardly stand the sound of a bass driver 8" or under; too earnest, too much popping of the driver when pushed. They just can’t handle LF and higher levels (Zero interest in arguing with people about this).

If you have poor amplification, you suck the life/quality out of the bass. If you have poorer cables, ditto. It’s a spectrum of performance, but also a spectrum of genres of bass technology - none of them definitively the best. YMMV