A 67 year old man with an 18 year history of type 2 diabetes mellitus presents for a routine physical examination. His temperature is 98.5 F, his blood pressure is 158/98 mm Hg and his pulse is 82/minute and regular. On examination, the physician notes a nontender, pulsatile, mass in the mid-abdomen. A plain abdominal x-ray film with the patient in the lateral position reveals spotty calcification of a markedly dilated abdominal aoic wall. The patient is taken to surgery and the abdominal aoa and proximal common iliac aeries are replaced with a graft. Which of the following aneurysm diameters is usually considered the threshold above which elective surgery is recommended, unless contraindicated by other disease?