I have used both LM 5W-40 and LM 0W-40. In my 1998 SAAB 900, LM 5W-40 was outstanding. Smooth, quiet -- great subjective feel. UOA indicated low wear rates for my 10k mile intervals. 0W-40 is not as good -- engine seems to run slightly rougher and louder. However, my fuel consumption went down slightly. UOA are slightly worse, although still excellent. They were close enough to 5W-40 to be within error margin.
Note that 5W-40 has BMW approval and 0W-40 does not.