When we're discussing Spring Drive MM600 and GS Divers we are talking serious Seiko hierarchy. I am not a diver (too old now) and I don't own an MM600, I do own both an MM300 and a GS SBGA031 Titanium Diver.
The MM300 with its Grand Seiko movement is a fabulous watch, I wear mine often. The GS SBGA031 is in another league altogether. The understated appearance, the feel of it on your wrist, the mesmerising second hand, the astonishing timekeeping, and the feeling of the overall quality just blows me away.
I always have to look at a Spring Dive Grand Seiko twice, the first time I am fixated by the sweep of the second hand, so I need to look again to see the time.