I single clutch downshift the higher gears (6th through 3rd), but I double clutch downshifts under that, or when skipping more than three gears. Call me crazy, but my gearbox has slower, notchy synchros, and double clutching lessens the load on the synchros, and makes the shift feel better. I'll double clutch heel and toe going from say 3rd to second while on the brakes, and anytime I go back into 1st when I'm not fully stopped.
The 370Z rev hangs more than my car does, so the trick is simply being more accurate with your timing, and a little less swift on clutch take up. On my car I over rev, and pull the clutch out as the rev's fall down. In the Z with Rev Match off, you have to nail the throttle blip a bit better, wait for the revs to slowly fall, or clutch out a bit slower.
Practice practice practice and you'll get it. The 350Z was IMO a bit easier to drive smoothly, but the 370Z can be mastered with enough practice.
*EDIT I just saw that you're in the Bay Area. Feel free to drop by Boardwalk Nissan in Redwood City (PM me first to make sure I'm here), and we'll go out and I'll show you a few tricks.
