Many of us consider the SL oil to be superior to SM...
and many of you would be be wrong...
All the test parameters are tighter for SM vs. SL, from engine wear to oil properties, and all of the hand-wringing about ZDDP has been proven to be nonsense in modern engines. Besides, I don't really view better cat-compatibility a bad thing since my cat system costs about 3 times what an new engine would cost.
That said, I'd use the SL-oil no problem, I just wouldn't use it for an extended drain. If I were putting it in someone else's car though, I wouldn't do it unless it met the spec, i.e. an older car.
Not all of us have ONLY modern engines, 33.3% of my fleet has flat tappet cams and 50% have no catalytic converters...