At those temps in my GH there is not allot going on with any of my slippers.
It's kinda hard to just generalize about Brachys and Parvis since they come from a wide geographic and elevational range.
Belatulum and concolor have the most northern range with some decent elevation and will tolerate the more extreme range of temps. The other brachy species are found closer to the equator and close to sea level and like continuous warm temps. (60,65 -90).
Similarly with parvis, micranthum and armeniacum are the northern species from the highlands dropping down to malipoense, emersonii/hangianum, and dropping further down to delanatii in South Vietnam near sea level. The micranthum and armeniacum can certainly handle sub freezing night lows, but low 50's is really pushing it for delanatii.
My micranthum did very little this winter at 55-59 for winter lows, and I didn't increase the light much either. I didn't see any signs of sheaths in the fall, and don't expect any blooming this year. But Leo gave a very good post on growing the cold parvis under lights in his basement, and gets good results only going as low as the mid 50's I beleive.