I own both of these, though I don't find any similarities between them whatsoever.
M7 is a great scent for cooler weather, and definitely seems a bit more "mature" and suited for romatic or more formal settings.
Dunhill Desire doesn't seem to get much love at all around here, but it'll always have a special place in my heart and I can't imagine ever being without a bottle of it. Several years ago, prior to my having washed up on the shores of Basenotes, it was the only scent that I owned. I bought it on a whim prior to a "first date" (which spawned dramatic, at times completely insane, and incredibly tumultuous "relationship") I've got so many memories associated with that scent, both traumatic and wonderful, and smelling it brings them all back with such a force that it almost summons a "fight or flight" response where I break out in goosebumps and the hair on the back of my neck stands up.
Needless to say, I don't wear it often... But I think it's a fairly unique and decent scent to own.