Proper cut-off voltage for SLA battery in 120°F+ environment?
Float voltage is lowered at higher temperature to prevent gassing. On discharge the open-circuit voltage is barely affected, but internal resistance is lower so voltage will be a bit higher at high current. At end of discharge the internal resistance increases and voltage drops rapidly, so a fixed cutoff voltage should be fine.   

If ambient temperature is normally 55ºF then battery life will be severely reduced. 

Deep Cycle Battery FAQ


  "Battery life is reduced at higher temperatures - for every 15
  degrees F over 77, battery life is cut in half. This holds true for
  ANY type of Lead-Acid battery, whether sealed, gelled, AGM..."