"Assuming you're at cruise altitude and there is not a runway available for an immediate descent and landing. . . "
I doubt that this criteria will be of primary importance when the cockpit starts filling with smoke. If there is no airport in the immediate vicinity, hopefully, practical survival instinct will prevail in getting the airplane down for landing on a road, in a field or on the water. . . before cockpit visibility reduces to zero.
After this UPS crash, the mind-set of having to land on a pavement at a suitable airport is no longer practical reality.
