I own the SHL5s in a large open living room. The main living space is 20' x 40'. I have listened to the M40.1 couple of times at my friend's place, also in a large room. Personally I prefer the SHL5s. For me, the SHL5s are about the largest speaker I would consider for a domestic listening environment due to WAF considerations. The M30.1 looked much better due to the smaller cabinet.
Sound-wise, I prefer the SHL5s over the M40.1s. There isn't any doubt the huge 40.1s throw a bigger sound and scale and go deeper in the bass owing much to the additional 12" bass driver and larger cabinet, but I prefer the "lighter" and more agile sound of the SHL5s. The bass of the M40.1s can be problematic in some rooms if not addressed properly, producing a lethargic sound.
I can live with the SHL5s alone although I used to have them with a subwoofer previously. After more than 4 years living with the SHL5s(which I love), I am looking for a smaller speaker in the near future such as the M30.1, instead of moving up to larger speakers. Personally I am leaning more toward smaller speakers after the obsession on huge fuller-range loudspeakers for the past one decade. The idea is they look more discreet and can blend in easier to the listening environment. They lose a bit of scale and bass but what they gain is perhaps a more sophisticated sound and better WAF.
YMMV