i havent seen too many people upgrade the calipers unless its being used for track days and stuff. heard that the skyline standard calipers are pretty sufficient at doing their job. people mainly change discs and pads, braided lines and new fluid.
these look pretty good http://www.shiftperformance.com.au/product...cts_name=Nashin 330mm Upgrade S15/R33&category_name=Brake Upgrades
come with braided lines, bigger discs and the mounting brackets for standard caliper.
but as shane said, porsche would be good or you can use these http://www.rocketindustries.com.au/descrip...?partno=PWR9023