The limitation is that bigger drivers will beam more at high frequencies. So the spectral balance - the sum of direct and reflected sound - will be too dark. You can compensate - sort of - by giving the driver a rising response on-axis, but that introduces new problems.
My favorite full - rangers have all been in the 5-8" range:
AER MK I
Supravox 215 BiCone
Diatone 610 MA
Jordon JX92 (a little sterile, to my ears, but I respect what it does)
I've only heard the WE 755a once; I liked it, but not at the crazy prices they're going for nowadays.
I spent the period from 1990-2003 looking for the "perfect" full range driver. Having since lived long term with electrostatics, and now, controlled directivity horns, I'm not that crazy about the compromises full-range drivers impose: limited power handling, problems getting deep bass and extended highs, poor off-axis response, potentially high distortion, etc. However, if I had woodworking as a primary hobby I might feel different - full rangers sure are fun to play with. They give you a chance to do seat of the pants engineering...for good and ill.