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

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 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.

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 

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

Western Electric 755

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