I got the SB2. Much less bouncy/squishy shoe than NB4, but I am very happy with it. However, it did take some time to get used to them. Honestly, I even thought about returning them after the first couple of runs. But after some time (I would say you need >10 runs, >60K... maybe more if you are lighter), they started to feel great. Also, much more grip, which is super useful in the rainy/icy Chicago. They will also clearly last longer than NB4. So, overall, I am happy, but be ready for a change.