Some interesting (and grim) questions have been brought forward here.
Over water, nearest concrete 3 hours away - do you ditch? When? Lacking additional information, if the smoke is so thick you can barely see, one must conclude that hull integrity or flight controls may be compromised, and ditching might be preferable to limping along.
How about windows? If possible, go low, depressurize the airplane, and open a window. Would it work? Would you freeze rather than burn?