Q45 front brakes are 2 piston sliding
Z32 front brakes are 4 piston fixed
stock are single piston sliding (front and rear)

The Z32 BMC isn't required until you really are doing full front and rear Z brakes. By then, you're pushing 12 pistons total compared to 4 stock. with Just Z brakes up front or just Q brakes up front, you'll still feel the braking difference. The Z BMC for just a front brake upgrade is mostly for people who use the open tracks. I run stock BMC, and pedal is good, i am used to it. for a track day i would need better fluid and pads, as i develop some fade and pedal stiffness from the generic pads/fluid i use (only on hard street runs).

KA24DEvelopment.com :: 240SX Brake Upgrades