I run both extensively.
In 140mm rear I run 160mm BOS Deville forks and feels nice and low, still pretty slack, and sprints nicely. I run it with an RP23 at the moment but likely to get a BOS VIPR to match the forks.
In 160mm mode, I've run it with air (BOS Deville and RP23) and coil (180mm Totem and CCDB). In air mode, it feels like a long-legged XC bike, which is ok but doesn't seem to be a big advantage over the 140mm mode in terms of plushness but you lose the nice'n'low feeling. In coil mode, it feels like a mini downhill bike, which is lush!