Which ARC reference component to upgrade?

Thanks for the interesting responses. I do have the Furman IT Reference 20 power conditioner and have used it for years after trying a number of others. In response to onhwy61 and Tobb, good question that has gotten me to think more about what the system does well and what it does not do as well. The highs, midrange and midbass are excellent, maybe the best I've heard in my audio room. Bass definition is excellent, but overall bass response is probably the weakest aspect of this system which seems to be similar to Lustformusic's comments. The Sophia 2s are replacing Von Schweikert VR4 SR MkIIs which had a fuller bass response with less definition. And lastly, on "upgrade itis" - no doubt about it. After many years of this hobby, I'm always ready for improvements which get me closer to the music. I'd say that is the fuel which Audiogon runs on.

After many years of this hobby, I'm always ready for improvements which get me closer to the music. I'd say that is the fuel which Audiogon runs on.

Indeed, that is the fuel that Audiogon runs on. Improvements....whether real or imagined. ;)

Get the Ref5se. It is quite a step up from the Ref 3. I have owned all the pieces you mention, 3 and 5, and 5se, and 110 and 150. The 5se will easily show it's benefits into a 110, which is still a great amp. But the 150 can't improve what wasn't there in the first place from the Ref3.