This is from The Brake Man at tbmbrakes.com from his Facebook page. It may make you think a little differently about aluminum calipers and multiple piston calipers.
12 RULES YOUR BRAKES LIVE BY:
1. Pad area (volume) has no effect on braking torque. Pad area (volume) effects life and heat management.
2. Caliper clamping force is a function of piston area (on one side of the rotor) times line pressure.
3. The hotter the brake pad gets, the faster it will wear.
4. Deflection anywhere in the brake system will result in a proportional reduction in clamping force.
5. Piston count has nothing to do with clamping force, piston area does.
6. Caliper deflection that exceeds piston O-ring retraction (around .020”) will result in brake drag.
7. Given the same design, aluminum calipers will always deflect more than steel, cast iron, or steel reinforced calipers.
8. If your pads are tapered, your calipers are deflecting.
9. All brake pads perform best in a temperature range. Too cold is just as bad as too hot.
10. The smallest, lightest rotor that will dissipate the necessary heat is the best rotor for the application.
11. A smaller bore master cylinder increases line pressure.
12. Larger diameter caliper piston(s) increase clamping force.