If it were me I would go for the extra power of the Ref 150. You can always upgrade it to an SE some time in the future if you want. I am not sure how efficient the Sashas are but the extra power should give you a bit more control. My Sonus Faber Elipsa SE are 92db and I have a Ref 110. I preferred the extra power of my Ref 110 (with KT120 tubes) over the Ref 75.
I would also consider upgrading your Ref 3 to a Ref 5se. The preamp can have more affect on the sound than the amp. And the Ref 5se is a huge upgrade over the Ref 3. I chose to keep my Ref 110 and upgrade my preamp a year or so ago. and again recently I decided to upgrade my phono preamp to the matching Ref Phono 2se and not upgrade my amp. Eventually I will upgrade to a Ref 150se but I feel no real urgency. At this point I am truly happy with the sound of my system.