A 68-year-old man presents with haematemesis and melaena. He is pale and sweaty. Observations show BP 92/60 mmHg, pulse 112 beats per minute, respiratory rate 22 breaths per minute and oxygen saturation 95% on air. His haemoglobin is 68 g/L. He has a history of stable angina. What is the most appropriate target haemoglobin threshold for red blood cell transfusion in this patient?