NGjockey and Aktchi,
My comments assumed large fullrange SoundLabs or possibly Quad 989 (or whatever its successor is). These big megastats have the diaphragm area to do deep bass.
I have four customers who claim to have measured their full-sized SoundLabs (M-1 or A-1) as -3 dB somewhere in the lower 20's. I was present for one such measurement, in which we got -6dB with the 20 Hz 1/3 octave band on a Stereophile test disc using a Radio Shack sound pressure level meter. The Rat Shack meter is down 4 or 5 dB at 20 Hz, so factoring that in we had a -3 dB point in the 20 Hz ballpark.
NGjockey, I understand what you're saying about the strings and bow but not the wood, and yes that applies to smaller stats but not to the big ones. I have a customer who plays voilin in a symphony orchestra in New England, and before the audition he told me that the only speakers he'd ever heard do justice to his instrument was his personal pair of highly tweaked Quad 57's. During the audition (he brought 90 CD's and it took 2 days!) he told me that not only did the big SoundLabs get the violin right, they also got the cello and string bass right, which he said he'd never heard any speakers do before.
Now I'm not saying big electrostats are the answer for everyone who can afford and accomodate them, but the big ones can do some things that the little ones cannot. And since the original poster was asking for comparisons with Eidolons, price-wise that left the door open for the big dogs of the electrostatic world.
In all fairness note that the planar magnetic Maggie 20.1 and hybrid electrostatic InnerSound Kaya have similar bass extension, and the big Maggie is less expensive than the big SoundLabs.
Duke