Brakes are not my forte: in this area, I speak more from theory than from practice. But I'll try my best:
1. Air in brake fluid biggest contributor to sponginess: probably yes, but there's also a vanishingly small density of air in the liquid where it will no longer be the dominant compliance.
2. Low-drag caliper: clearly to go from low drag to high drag (i.e., applied brakes,) will require an increase of force and some displacement of fluid. The real question is partial F/ partial V.
3. How much sponginess for a floating vs. fixed caliper? I haven't the foggiest idea. It comes back to the definition in (2.).
4. "Wedgeness": The pads don't wear exactly parallel to the rotor surface since the distribution of clamping force (and thus pad wear,) isn't uniform across the pad, but higher on the pad's leading edge. Some of the partial F/partial V involves displacing some additional fluid to restore the pad face to a parallel alignment with the rotor surface.
5. How rigid is a stock metric g-body front caliper (or any other caliper for that matter): I haven't the foggiest. Probably 1e9 N/m if not greater!
6. "How do you maximize..." I don't know, which is the reason why I only offer restricted comments on the topic.
Last edited by MAP; 02/03/12 10:50 PM.