While 55F is nominal lower limit for Vandaceous orchids, the Rhynchostylis are probably OK down to 50F. Coelestis is known as a cool grower, and gigantea is fine with intermediate temperatures. Retusa is the warmer member of the genus, but mine is doing fine with 55F nights.
Very nice. Two spikes on that size plant... very impressive. You must provide great culture.
I'm really like this genus but I think mine are far from blooming.