I've spent years playing bass in orchestras and also recording them. I've also spent years looking for the best classical recordings, like a lot of people on this list.
What I have found is if you really have a good recording, very few speakers will hold up to it, not because of bandwidth alone, or inner detail, but also due to dynamic range.
I like to play the system at the volumes that the recording was made at.
My room is about 21' by 17', with carpets, stuffed furniture and LPs lining the walls. Its reasonably dead. One of the best recordings I have run into is the Soria Series (RCA) recording of the Verdi Requiem (Dies Irae side one). The dynamic range, subtlety, detail, bass impact, natural presentation and the like are matched by few recordings, especially anything recent. In a nutshell, most systems simply cannot play this record- it is simply too demanding! It can literally go from a whisper to so loud that many will be diving for the volume control so as not to damage something.
I find that if you need a transistor amplifier to get the sufficient power to drive a speaker to lifelike levels, it will never sound like real music; at best only like a good stereo (Ho hum). So its tubes all the way for me.
That limits the speakers- tube power is expensive and tricky to get right!
The Classic Audio Reproductions T-1 or T-3 is the best I have seen. They are efficient- 97 db, easy to drive (16 ohms), full bandwidth (20Hz-45KHz), easy to set up (6" from the rear wall in my room), image easily, detailed enough to match the best of ESLs and cone systems, hard to fault really.
I can play them to any level I want and not strain the amps. Lots of local artists wind up bringing test recordings over to see if anything that they are working on needs tweaking. They are quite revealing.
This is the only speaker that so far has allowed me to play my most demanding LPs (CDs have never proven as demanding BTW- they just don't have the impact!). Verdi Requiem, not a problem. Black Sabbath 'Paranoid' (original German white label Vertigo pressing) no worries (most systems haven't a hope of playing *that one* at anything near a normal volume BTW). Wagner's 'Das Reingold' on Decca with Solti conducting- easy. 'The Wand of Youth' on EMI-piece of cake. Schwartzkopf singing the Four Last Songs of Strauss on EMI- fabulous! These are awesome recordings, the sort of thing that if they are done right make you shiver- or cry.
Most speakers that have the resolution and bandwidth to really do the job usually lack the ability to also be easy to drive. The CAR is the first (and after 10 year still the only) that I have seen that can do everything right in the same place at the same time.
BTW- they are great with rock, jazz and anything else you can dig up too.