Upgrading from Thiel CS3.6 to Avalon

I'm considering upgrading my 20yr-old Thiel CS3.6 to Avalon Opus or Eidolon. Do you guys think it worth the upgrade? My listening room is measuring 17(W)x13(L)x8(H) ft.(speakers along the long wall) Which one(Opus or Eidolon) makes a better choice?
BTW, my other components: Esoteric K-05, Gryphon Diablo, audience Au24e XLR and cables.
I don't believe it is an upgrade. You will lose the phase and time coherence and you will know it when it is missing. If you're at all like me, when I moved away from Thiel to Dynaudio for a couple of years, I moved back because I missed that pinpoint positioning of instruments and accuracy of timbre that the Thiels furnished.

Why not truly upgrade to 3.7s? Or Vandersteen 5As?
I went from 3.6s to CS6 and to Salksound Soundscape 8. I am very happy with my latest purchase. IMO, The Salk is much better in every way.
I've owned the CS1.5, CS2.2 and the CS2.3; you will find out that the Avalons' are much smoother, very coherent and projects a more stable image/soundstage. No forwardness or hardness in the midrange area YMMV...

IMHO, Avalons' are superior...
Overall, I have to agree with Stevecham. If you gave the Avalon's a thorough demo, and you know you really like them, that's fine. Otherwise, I wouldn't buy any new speaker. The ones you are looking at are just too expensive to take a chance on. Also, I would consider the 5A's, as well. Not surprising because Vandersteen is my favourite speaker.

Thiel speakers are a unique beast. Upgrade to the CS 2.7 or CS3.7 model.

Keep me posted on your decision.
I owned Thiel 3.5s for ( 8yrs ) Loved Them! Drove them with Forte' monos (Nelson Pass design) and Spectral electronics. Thiels; at least the Legacy models are as you know, as an owner, are what everyone claims. Very hard to find a speaker as good or better for the money. I tried Pro Ac, Wilson, Sonus Farber but finally settled on Avalons. Opus w/ carbon woofers. The Eidolon come up for sale fairly often, I have never seen a pair of Opus for Sale. The Opus will fit your room well ( my room is 13w X 23L  X 9h ) My opinion- The Avalons are superior. Better imaging / soundstage. Smoother top to bottom, no need for a subwoofer. wigs comments also apply. The Eidolon; I heard both at the dealer many times and (6wks) in home demo. But I settled on the Opus. They will fit & fill many rooms. Your equipment should mate well. Now that Jim and Kathy are gone. ( even though Thiel seems to be supporting the Legacy models ) I think you will find the Thiels to be getting long in the tooth and service to become problematic in the future. 
If you can find a pair of Opus w/carbon woofers ( ceramic lack in the bass) You will never look back.

Best Wishes on your Journey.