The Ref 150 has slightly larger transformers to better utilize the new KT 120 tubes. You can also use the KT 120 tubes in the ref 110. The Ref 110 will sound a little better and give you a bit more power. Because ARC changed the transformers for the Ref 150, the Ref 110 is not upgradeable therefore the changed in model number. I have not heard the Ref 150 yet but I don't think that the difference will be significant. If you have a Ref 110 than I would consider using the KT 120s the next time you re tube.
