That Z is a beautiful machine. Love the motor work and the "sleeper" look to it. The M...well...it's an M...the best of the best. lol
#1 Is a good shot but don't use Imageshack to host such large files...took forever to load lol. Also, you could flatter the car a bit more by doing some touchup work on the body, i.e the front skirt has big scuffs and paint issues...clone those out for him. And I can't believe he didn't take the front plate off for a car show lol
#2 shows too much, stand where you were, but zoom in to fill the frame with the engine bay, and avoid your own reflection. Maybe some fill flash too, you lost the valve cover and deeper in the engine bay is black (no details).
Also, maybe (if the owner will let you) have someone hold the hood up (out of frame) and put the brace down. It's an unattractive line that throws off the balance of the shot.
#3 would be killer if you got lower, almost hub height to the wheel, show the brake caliper/rotor behind the wheel. I'm assuming the calipers are either upgraded or factory badass....show that!
#4 is a snapshot. To make it a good photograph, move the car so nothing is in front of it (get rid of the car/people in the shot), lay the front seats all the way back so you can get the bottom of the seats and shifter...up through the windshield...filling the frame from dead center behind the car. This would be VERY easy since it's a convertible, and would show the cockpit and how driver-centric the M's are. The factory leather seats are kind of "bleh" IMO, but if you want to show them, by all means lol
Hope that helps, thanks for posting photos of some great cars!