Here's my Q,
What is going to make the biggest impact on how well brakes work? IE, friction area on the disk, area of the brake pad, or total area of the caliper piston(s)?
I'm doing my home work before I start looking for parts for my P510. I'm not realy sure (yet) if I'm better off with big rotors, pig pads, or big four pots. To further complicate my decision, I want to stick with 22mm(ish) rotors. (to keep the weight down, that big turbo nissan stuff is much too heavy for the weight of a P510)
I have a pair of 280ZX rotors, which are 265mm, and have a friction area 55mm wide. BUt my calipers are incomplete. Then there's S4 RX7 stuff, which is a 280mm rotor, with a 4pot caliper. But the pad area is only 40mm tall. Of maybe the rotors from a SR20DeT S13, which are also 280mm, but I'm not sure how tall the friction face of those is yet. The plain S13 rotors are only 250mm, with a single piston and 40mm talll pad. They fit under an alloy 13", but I've got 17's so I mite as well got as big a is practical.
So which aspect do you think has the greatest bearing?

optimum temperature....based on your cars weight speed and the way the brakes can exit the heat energy.
too big a brakes with carbon metallic pads on a light car which just goes to the shops is just as bad a situation as drum brakes on a dodge viper race car.
then come the issue of unsprung weight. Big discs and calipers is gonna upset your handling significantly.
I had more than adequate brakes on my 1200 coupe race car with semi metallic pads and stanza solid discs.
My next car had brilliant Willwoods on the front with a booster which was overbraked...i had to take the booster off...its up to you application.
For street application i would go for a converted GTR HR32 setup (fit under a 15 inch rim) for race i would try a set of brembos off an evo9 or something similar.

I believe the biggest impact on braking would have to be pad size and number of cylinders. This is disregarding racecars.

To double your stopping power just by increasing rotor size, you would have to double the rotor size. This is far from practical on our little datsuns that run 13-15in wheels.

On the other hand if you were to go and get a standard small rotor with a single piston caliper and substitute in a z32 alloy 4 piston caliper your braking would preformance increase about 10 fold.

AS i said above this is disregarding a racecar setup, where heat dissipation is the key factor. A combination of a medium sized vented rotor and a good 4 piston caliper would be excellent.

My 1600 used to run 280zx vented rotors and hilux 4 piston calipers and it was wonderfull on the track

That would be a good combo, but aren't the 280ZX rotors too thin for the hilux calipers? Wouldn't you be running the risk of having the pistons extend too far when the pads are nearing the end of their life?

Undoubtedly it is tire patch. Even stock 1200 disk brakes do well with a wide tire. On the other hand, the best MK3 brakes won't stop fast on skinny tires.

Hey bart when measuring the brake pad area don't forget length, you want the total area. The Rx7 brakes might only be 40mm TALL compared to 280zx stuff but i'd say its quite a bit longer pad compared to the 280zx because they are 4 pots.
Also going back to the unsprung weight thing, a 280zx caliper is F*cking heavy. I was mucking round with john's R33 skyline 4 pots to see if they could fit the 280zx struts and I don''t think there was bugger all weight diference between the two! (calipers only, rotors would be a different story)
My ultimate bang for buck setup which would stop well, weigh bugger all and looks the nuts would be:
S4 R7 4 pots approx 250NZD
willwood 10.5" rotors with bolt on alloy hats to reduce the unsprung weight. rotors are about 90USD each and alloy hats and caliper mounts would be free because I know a guy :)

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Stock 1200 discs are borderline at best. Even with good front tyres, trying to pull up from 120-130 is a really big ask

Nick,
Yeah I've been talking to a guy locally on a rotor forum. He's got some S4 stuff he'll do for a couple of hundred. You are rightthough, the ZX rotors are mighty heavy. I have a jig to redrill 114.3X5, into 114.3X4. So I could redrill the S4 rotors to 4 stud. Or I'll use the 280mm S13 rotors.

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i was running the earlier non vented type hilux 4 pistons on the vented 280zx rotors. They just fit, but i dont know about if you had brand new rotors, mine were worn already