Bear in mind, 120F output in Slantfin's documentation is average water temp (AWT), not boiler output temp, and somewhat optimistic when projecting output at AWT below 120F. Below that temp the output becomes increasingly non-linear, and is more affected by things such as dust-kittens, abutting furniture & drapes, etc.
Since you can meet the load at design temperature with an AWT of ~120F it'll always be in the condensing zone. The amount of additional benefit you'd get by finely tuning the outdoor reset curves are small, so don't try to get the last 0.5% of efficiency out of it with temperatures where output is unpredictable, (say, and AWT of 95F or something) which would likely lead to large room-to-room temperature differences, and you'll start short-cycling the boiler. With taller convectors or old school radiators you can go that low, but not with low-rise fin tube.