brake performance

Well that depends on what sort of brake "performance" you're talking about.

Stopping distance: Depends mostly on your tires. Brake upgrades won't change this much.

1977 Frnt Calipers

Fade resistance: Depends partly on rotor cooling and partly on pad compound. Vented rotors and good pads will help with this. Calipers have no effect.

Pedal feel: The pedal will take less force but longer travel to achieve the same brake torque with the Volvos compared to the 323i calipers. You may want to change the master cylinder to a larger bore to make the travel shorter again. Once you do that there is probably no difference in the feel.

The size of the pad area only effects how long it takes to wear the pads out. It does not effect the braking torque and probably has minimal effect on the feel.

http://www.massivebrakes.com/kits/e21/front/300/32/

Basically you need vented rotors, good pads, and good fluid. Caliper choice is 1/10 as important as any one of those. Front 323i calipers are identical to '77 320i calipers, and their only advantage is that you are able to run a vented rotor.

Braking torque can be a consideration, however, how much does brake torque matter once they've been locked up if you don't have ABS None. Once you start running bigger&stickier tires, it becomes harder to lock the tires up, so then more brake torque is needed. Until you get to that point, bigger brakes will just have a longer life and stay cooler (definitely advantages to both of those) and will likely have more un-sprung weight (not so much of an advantage).

1977 Front Calipers

Rotors need 2 things, mass to instantaneously absorb heat during a braking application (heavier is better), and some way to cool them before the next brake application (venting, possibly with air ducting/diverting). The stock non-vented rotors have very little of either of those things.

i do know that with stock vented rotors, calipers, hawk hp plus pads and ATE fluid, i can overpower the summer tires i'm running.

Pads: Hawk hps brake pads are about as good as it gets.

Torque is a measure of the turning force on an object and is greatly influenced by the length of the lever. the longer the lever the greater the mechanical advantage. therefore a bigger diameter rotor has more torque. i really don't believe pad size makes much difference with torque. (larger pads = longevity!)

Wilwoods brake calipers usually have a larger pistons (and several sizes are available) which does increase brake torque for a given line pressure, but you can always just press harder on the pedal instead. Wilwoods are also much lighter which is kind of a big deal since they are unspung weight (attached to the movable part of the suspension). But yeah, any brake upgrade that uses the same rotors is mostly for cosmetics/bragging.

there is a good discussion over on the forums regarding the upgraded girling calipers...its worth reading...it can be found here...

http://forums.bimmerforums.com/forum/showthread.php?t=308282