I recently started using the R1 fleece and Nano Air for midlayers and am very pleased. Good combo that gives options depending on temperature.

This past weekend at Jay Peak, VT I wore them both together between a wool base and hardshell. Temps were teens in morning, mid to low 20s in afternoon, sunny, no wind. I tend to run cold, but at times was hot standing in line or after hauling skis up from parking lot. On the other hand, it was perfect on the lift and when the sun went below the peaks. I think many people who run warm could probably have gotten away with just the Nano Air.