Spica's TC 50 vs. Sound Dynamic RT 3's

The spicas are wonderful speakers but do need to be away from the rear wall to image best. IF you find a pair on Audiogon (or elsewhere) for a reasonable price I would get them and see how you like them ... worst case is that you lose the shipping since they're really easy to sell on. I have not heard (nor heard of) the RT3s so I cannot comment on relative performance. Hopefully another poster will fill in this information.
Since your main system is ESLs I find it hard to believe that you would not like the spicas if you have the room to keep them away from the rear wall by a couple of feet. SUre they're not ESLs but I think the design goals were similar ... imaging and midrange rather than bass and SPL.

I've had two pairs of TC-50's. The first was the original and the second has slightly better connectors, a cross brace, different felt configuration around soft dome tweeter and supposidly better power handling. The later model TC-50 was better. The TC-60 was completely different and I have never heard it. I modified my TC-50 with less internal "stuffing", internal wire replaced with cardas wire, new edison price connectors, removed the felt on the front. The sound of the TC-50 does have some coloration, kind of a signature midrange sound, excellent sense of space, imaging, phase coherency. Bass is very tuneful but unless you're in a small room bass can really lack (my current setup suffers from this). I find they sound best with cardas cables (they can sound too lean with the wrong cables). I don't have a tube amp but they did sound better on a tube amp I heard them on. They have a 4 ohm load so If you have a true class a amp like mine then their otherwise poor efficiency is alleviated somewhat. The spicas overall can really compete in terms of revealing detail, space, imaging even with real expensive pieces but have some harshness, coloration, damped bass compared to good proacs, charios, others.

IF you are used to the Quads, gotta go with the Spica's. Rt 3's are good, but the midrange on the Spica's just sneaks up on you letting you know how good it is. I would have to say the RT 3 has better low end, and actually more extended on top, but in the midrange and depth dept, and now that I think about and read a little more(I keep notes on everything I have ever listened to at home)in the focalazation and placement, Spica has it and really a lot of other speakers in the same price range. was one of those speakers that got it amazing right at the time.
Caveat though, Original drivers no longer made for the Spica, and the woofers had very tight tolerence's in the voice coil, so if you buy a pair used, make sure they are extremely well packed. Company in PA will rebuild the woofer cheap($40) but they are so busy it takes over 6 weeks to get them back.