BEST fullrange speaker drivers in existence, 4"-10" diameter range, and...Go!

Definitely the Cube Audio 10 incher with 3 whizzer cones and Hifi Collective in the U.K. have them in stock for Xmas!

Western Electric 755

It has the most details, natural and 3D soundstage.

Very very few masters of first Order slopes in multi way design, even fewer in business and or still alive
my bias is Vandersteen, but I own more than that....
scanspeak makes a driver used in the Quattro - not inexpensive....
the physics of a single full range driver are daunting , leaving it at that....
now diving IN is good
i did that back in 1982 running a FFT on a Commadore PET trying to better what mighty KEF could do
skip the el cheap iron core indutors is my first clue !
ha

have fun

I would heed the advice of Johnk,  his comment makes much sense and reflects wisdom. Cube Audio (Poland) produces very highly regarded 8" and 10" full range drivers. Not cheap but are considered world class quality. 
Charles 

I use single 4" Merrill drivers in my Zigmahornets.  I would never think of doubling or quadrupling these.  The imaging is amazing and you won't get that with multiple drivers, just more sound.  Most single drivers tend to be very efficient with power.
The lack of a crossover is very clearly a benefit with this design.
Another option would be a coax driver to maintain the absolute best imaging (in my opion).  Seas makes a wonderful 6" coax that can be biamped/biwired or single wired with a jumper.  The crossover is absolutely minimal in their design.  Not a cheap option but amazing sound.

your idea of using large fullranges in multiples is highly flawed rethink read study up on design instead of making such mistakes you could use a few 4inch but even thats not the best way loudspeaker design is not easy its not just slapping parts in a box

I would check out the Pure Audio Project Horn 1 compression driver. I think its about 40 Hz to 20K. They also have the Voxativ versions (there are three, but VERY pricey).

effectively i must distinguish for myself whether or not, all other things being equal, that horns either are or are not decisively better (aka more "musical") than even the best speaker cone driver

ok, to clarify:

looking for the best midrange driver there is, for a DIY project that will include 2-4 of these per side.  I am specifically looking for a fullrange driver whose ~400-4000 Hz behaviour is reference standard. im testing some ideas about lower order crossovers and I have literally no idea what I am doing (yet)

And, are you asking for off the shelf drivers you can purchase separately from a finished speaker system?

Here you go
https://voxativnewsitedemo.squarespace.com/products/acxhb

Not clear what you're asking. What do you mean by "fullrange"? Is this for a DIY speaker? Do you mean bass extension? Or single driver that best covers 20-20K cycles?