Well my wife's Warrior (my old ride) has pretty much every mod you can do without cracking open the case.

My buddy raced me on my KFX which is totally stock. Off the line we were even but as soon as I hit mid-second gear I pulled away. By 4th gear he was at least 5-7 bikes behind me. He weighs about 175, I weigh almost 300. So the weight issue didn't not matter.

My guess is the Z will beat you pretty easily. A 400ex would be a good race though, I used to run right with them on my Warrior.