Okay, I tested the cold water extraction. I had added 30ml per gram, and I drank 90ml (so for 3g) with 230mg harmalas.
The strength is excellent. It was considerably stronger and lasted for longer than the same amount in a normal brew. Usually the effects last me for 2h, with the CWE they lasted almost 4h. It felt similarly strong to my pharma dosing (40mg DMT initially and then redosing with 30mg), although it's difficult to make comparisons because the character of the experience is noticeably different.
However, my hopes that it would deliver a more digestible brew didn't materialize. While it had absolutely no sediment without decanting (a major plus), it seemed to have as much tannin as the boiled version. I didn't have much nausea, but I had a very strong stomach pain for almost all the experience.
I think CWE is superior to boiling: the method is simpler and the result seems stronger and especially longer lasting. However, I continue in my search for a way to drink mimosa without too much stomach pain.