Lots of stuff here in the archives about those speakers, but surely a lot to weed through...I will try and help with what I personally have played through. I just bought a mint E-120 and Swapped it out in my 1x12 cab just tonight. It was dripping with killer tone. It is what I have been looking for, I love it. I also have a K-110 2x10 cab I like to play through too. It has less bottom end than the 12" E stuff, but crystal clear and spanky. They are 70 watt speakers so 2 will do a 50-80 watt amp just fine. They are hard to find and when they do pop up get ready for a bid war.I saw some E-110's go for 80-$100 just yesterday. The E110's take a crap load more power, and like the 12" have a better bass response than the K-110. I am sure they are the shit. They are much heavier though....
I now can say the difference in the Eminence Commonwealths V's the E120 is there is less bass response in the E's than the commonwealths, but sound very similar. The commonwealth has a fuller sound, maybe because they are newer, more mid response too, but sound remarkably similar. The E-120 IMO seemed to be such a perfect fit with the rig to get the tone I'm after, emmi's do it too with a little more lower end which can be nice at times. I like the E-120 the best out of the lot at this point. The Black Widdow sounds remarkably like a K-120, or at least mine does, bright, clean and crispy, but a little different than my E-120 which like I said has a notable increase in bass response. I think the E-120 is an improvement on the whole for loud playing, filling in the spectrum a little better. The increase was not unwelcome or overbearing ever, like the emmi's can be sometimes. If you are considering K-110's you'll love them. I will have some E-110's soon enough.
I would reconsider the D- stuff, extremely expensive, less wattage and more fragile. You can't deny their great tone, but the latter year JBL's are fantastic speakers too and much more rugged, plus significantly cheaper.
To sum it up: all my speakers I use or have recently with my Jerry style rig:
K-110- bright crystal clear clean top end, easy on the bass and mids
Black widdow/K-120- much like the K-110 but a bit more bass response, yet still very bright
Commonwealth- heavier on the mids and low frequencies, an even amount of brightness but not its inherent quality- tone is similar to the E
E-120- the perfect ground between the K and commonwealth, bright and with the perfect bass and mids response for me. BUT HEAVY
stock fender emmi's in twin- mediocre at best response all around.
PS- all of this may be no good to you depending on your amp, but I would jump at the E-110's in a heartbeat or keep fishing for some K's if you like stuff a little brighter. I hope this helps....