As a copilot I used to fly with skippers who'd flown the Convairs, both the '880 and '990. I remember them saying that the normal cruise Mach was 0.92 but as fuel was cheap in those days they would simply accellerate until the bell rang, then ease the power off a bit. I think Mmo on the '990 was .96 or .97 after they fitted the "Kucheman carrots" on the wings to cure the prohibitive drag penalties discovered in flight testing.